I don't know about the
LotR wargs, but I did find this:
http://www.heresy-online.net/forums/showthread.php?p=899816 Near the end of the page someone has done some pretty good work with wolves from the vampire counts range (I think).
Painting them so they look slimy or otherwise "not natural" is probably going to be the way to go with any conversion you end up doing.
I've been thinking about how to make those as well. The chaos hounds + some random tentacles and greenstuff is what I'm leaning towards.