Don't give up! A stall is just a temporary lull in training .. many dogs (and people) need these lulls in order to let the information sink in better. Training some behaviors can be a lesson in patience for us humans.
I, too, learned the ear pinch method initially as that was what was taught two decades ago when I started training. But I moved away from the forced retrieve successfully and my current dog (a chow - NOT a breed high on the "natural retriever" list) is doing competition retrieves that were purely positive trained.
The Clicked Retriever is an excellent place to start. If he's happily taking the dumbbell into his mouth, you just need to vary things a bit - but use LOTS of patience. Will he take it from your hand when you hold it above his head, below his head, to the right and to the left? Add these in slowly, and gradually expect him to reach farther and farther for it. It can be difficult for some dogs to understand that they need to reach down for it, so I would bring the dumbbell up to eye level and then move it down below the chin, immediately encouraging the dog to take it.
You may need to have him start to take the dumbbell off of a stair or a chair - something that's above floor level but still has him picking it up instead of taking it from your hand. Some dogs get stuck on the concept of your hand being part of the signal. But if you can stick the dumbbell in front of him on a chair and get him to take it, that's a step in the right direction. Stairs work nicely because you can start with a higher stair and then move to a lower stair (and eventually to the floor).
Try sliding the treat into his mouth as you take the dumbbell out. You may want to use a verbal "YES!" with this instead of the click, so that you can say "YES!" as you give him the treat (to avoid having him think that he can drop the dumbbell when he hears the marker sound/word).
If he'll hold the dumbbell, try having him step forward one step before you take it. For a dog, holding the dumbbell and actually moving with the dumbbell can be completely different. You may have to break it down into really tiny steps.
I taught a positive retrieve to one of my chows who had ZERO (and I mean zero!) retrieving instinct. She was 14 months old when I got her so I missed the early stages when I might have been able to reinforce toy play. But with persistence I was able to get her to pick things up for me, and now she will run over eagerly when I pull out the dumbbell. It took a long time for her because of her lack of retrieving instinct, but I proved to myself that this method can and does work on dogs even if they don't naturally want to retrieve.
Good luck!
Melanie and the gang in Alaska