I want to say that 2Thick did it on Elite and had a link to it on his homepage but that was a while ago. Plus he had massive traps.
Here's my opinion on spot injections. I truly believe they work from experience. ....BUT... I believe the reason they work is because of muscle fascia stretching, not anything to do with the actual compound being in that body part.
For example, I don't think injecting your quads or glutes will help at all. I believe it can help delts, bi's, tri's as if you push 2-3cc's into any of those respective body parts then it will be much bigger than it's ever been thus stretching the muscle fascia beyond where it's ever been before. I translate it similarly to muscle memory. When you get big and then take a break it's always easier to get it back then when you've never been to a certain size and you're trying to get there.
I did mostly delt shots last cycle and I know it helped a lot because my delts improved more than anything. I'm now doing some bi and tri shots to see what it will do for them. So far my bi's are the biggest they've ever been.
With that said I'm not sure how much it would help traps.