Doesn't help you at the moment, but I have one in the works where Cas is a church-foundling raised as a hunter-priest by Pastor Jim... who makes a deal when Meg kills Jim and becomes the Righteous Man who angel!Dean pulls out of Hell... Bobby puts him in touch with Sam (who he knew before Hell in a "they got stuck together when Jim and John went hunting" type cousiny-way) when he gets bought back and it pretty much follows along the major arc of season 4 from there.

Unfortunately, it is very much "in the works" and I don't post WIPs (don't trust myself to finish them any more) so... it might take a while. :/