I've just found this. I don't know how I missed it when you first posted, but I did. It's probably in my memories under 'not read'. I went through a phase where a lot of fic got shoved in there.

I found it through a rec on spnstoryfinder for AUs where the boys weren't raised together.

So far, this rocks so hard that I don't know what else to say. I'm sure something will come to me as I read further. *G*