I think it had something to do with the Juhaniґs "feat" that allowed her to sneak without a generator.
That's done with a "hide item". Basically there are hidden item slots on creatures and characters where items can be equipped, but don't appear visible in-game. For Juhani, she has a hidden stealth field generator belt. Most creatures have hide items on thier hands so that they can, for example, poison people on attack. I used the same technique for my Species Specific Feats (
http://www.lucasforums.com/showthread.php?t=183411) mod (thread for how I did it (
http://www.lucasforums.com/showthread.php?t=181550), thanks to Stoffe).
I've tried adding the generator to a clothing item before, and it didn't work. Maybe try adding a base item that references the armour column (model C for example) instead of a belt.