You could consider buying a Carmine Dragon or a Warpfire dragon from Forgeworld and using the wings. It's a much more expensive rout to go but the wings are suitably chaosy and you'd have an easier time of making something look like nurgle.
Nurgle is tough when it comes to flying things I find...the idea of flight is really difficult to wrap your head around when you're talking about large, bloated sacks of pus.
You might try something with paper mache around a balloon to get more of a blimp look to your creature. That way it looks like a giant floating ball of disgusting gas instead of something flapping its wings.
http://www.warseer.com/forums/showthread.php?373907-Scourge-Drones-Counts-As-Nurgle-Heldrakes
this page also has some good ideas.