If that is even possible.

http://www.fanfiction.net/s/5150722/1/Xavey

have you tried the Black Library forum? Some of the stuff on there used to be dubious.

Or just read the published stuff by CS Goto or Gav Thorpe!

Managed to find a few that might raise some red flags, but I've wanted to run them by someone who knows the canon better, first. Warhammer's section on the Pit is pretty disappointing, actually.

Specifically, if there are any with the forces of Nurgle as antagonists.

Chliever's from a 40K badfic, I never really intended there to be a concrete one he was from, but if you could find one, that'd be great. I'd write a mission for it, explaining our favorite Daemon's recruitment.