Some dogs see their ability to demand attention as confirmation that they are the "alpha", then become difficult to handle when told to "sit" or "down" or some other demand is placed on them. It is not their leadership status that stresses them out, it's the lack of consistency. They may or may not actually be alpha material, but having no one in the pack that is clearly the leader is a bigger problem than having the dog assume that role full time. Dogs are happiest when the pack order is stable. Tension is created by a constant fluctuation of pack leadership.
Your dog already knows that he can demand your attention and he knows what works to get that to happen. As of today, it no longer works, but he doesn't know that yet. We all try harder at something we know works when it stops working. If I gave you a twenty dollar bill every time you clapped your hands together, you'd clap a lot. But, if I suddenly stopped handing you money, even though you were still clapping, you'd clap more and clap louder. You might even get closer to me to make sure I was noticing that you were clapping. You might even shout at me "Hey! I'm clapping like crazy over here, where's the money?". If I didn't respond at all, in any way, you'd stop. It wasn't working anymore. That last try -- that loud, frequent clapping is an extinction burst. If, however, during that extinction burst, I gave you another twenty dollar bill you'd be right back in it. It would take a lot longer to get you to stop clapping because you just learned that if you try hard enough, it will work.
When your dog learns that the behaviors that used to get him your attention don't work any more he's going to try harder and he's going to have an extinction burst. If you give him attention during that time you will have to work that much harder to get him turned around again. Telling him "no" or pushing him away is not the kind of attention he's after, but it's still attention. Completely ignoring him will work faster and better.
YOU HAVE THE POWER
As the human and as his owner you have control of all things that are wonderful in his life. This is the backbone of the NILIF program. You control all of the resources. Playing, attention, food, walks, going in and out of the door, going for a ride in the car, going to the dog park. Anything and everything that your dog wants comes from you. If he's been getting most of these things for free there is no real reason for him to respect your leadership or your ownership of these things. Again, a timid dog is going to be stressed by this situation, a pushy dog is going to be difficult to handle. Both of them would prefer to have you in charge.
To implement the NILIF program you simply have to have your dog earn his use of your resources. He's hungry? No problem, he simply has to sit before his bowl is put down. He wants to play fetch? Great! He has to "down" before you throw the ball. Want to go for a walk or a ride? He has to sit to get his lead snapped on and has to sit while the front door is opened. He has to sit and wait while the car door is opened and listen for the word (I use "OK") that means "get into the car". When you return he has to wait for the word that means "get out of the car" even if the door is wide open. Don't be too hard on him. He's already learned that he can make all of these decisions on his own. He has a strong history of being in control of when he gets these resources. Enforce the new rules, but keep in mind that he's only doing what he's been taught to do and he's going to need some time to get the hang of it all.
You're going to have to pay attention to things that you probably haven't noticed before. If you feed your dog from your plate do you just toss him a green bean? No more. He has to earn it. You don't have to use standard obedience commands, any kind of action will do. If your dog knows "shake" or "spin around" or "speak" use those commands. Does your dog sleep on your bed? Teach him that he has to wait for you to say "OK" to get on the bed and he has to get down when you say "off". Teach him to go to his bed, or other designated spot, on command. When he goes to his spot and lays down tell him "stay" and then release him with a treat reward. Having a particular spot where he stays is very helpful for when you have guests or otherwise need him out of the way for a while. It also teaches him that free run of the house is a resource that you control. There are probably many things that your dog sees as valuable resources that I haven't mentioned here.
The NILIF program should not be a long, drawn out process. All you need to do is enforce a simple command before allowing him access to what he wants. Dinner, for example, should be a two or three second encounter that consists of nothing more than saying "sit", then "good dog!", then putting the bowl down and walking away.
ATTENTION AND PLAY
Now that your dog is no longer calling the shots you will have to make an extra effort to provide him with attention and play time. Call him to you, have him "sit" and then lavish him with as much attention as you want. Have him go get his favorite toy and play as long as you both have the energy. The difference is that now you will be the one initiating the attention and beginning the play time. He's going to depend on you now, a lot more than before, to see that he gets what he needs. What he needs most is quality time with you. This would be a good time to enroll in a group obedience class. If his basic obedience is top notch, see about joining an agility class or fly ball team.