If it's a crowding issue, try changing the location of the reward or get a transition plan going to remove the reward from sight all together and use markers.
When my dog was crowding, I noticed it was because I always placed the reward towards the center of my body and he would push against me in an attempt to get closer to the reward. Don't know if your situation is similar but it might be a good idea to move the reward around and see if the dog is focused on that rather than the handler.
I've since moved on to markers and the reward is out of the dog's sight.
What I did to correct the crowding was train with food for a little while to get proper body position. I would feed him directly above his head only when he was in proper position. When halting (and he is expected to sit) I would lift my hand slightly and push it to the outside of the dog (sort of hard to explain, doing my best
) so that his butt sits straight and then feed him if he's in proper position.
At the same time I worked on markers so that I can keep the reward out of sight and have him focus more on me and such.
So now, I have the toy in my pocket before I enter the field. I'll cue the dog (I use "Are you ready?") and ask him to fuss. As soon as he's in the proper position I'll give the marker (OK) and whip out the toy. Now whenever I say "Are you ready?" His eyes light up and he gets focused (watching me, etc) and you can see he knows its time to work. From now on, whenever I start to fuss I would put the toy in my right pocket where he can't see it and will release the dog before rewarding.
Don't know if you tried all of this or if this is helpful at all, but I hope it helped a little bit.
Some say making large circles to the left helps but it didn't for me. He learned that a knee to the head was just part of heeling rather than see it as him being in the wrong position. I;m sure lots of it had to do with my handling though...