I figured this out myself, but I'm sure it must have been here before. Tried a few searches, couldn't find it though. So here it is.
EDIT: Must be in any CoT instance that turns you into a human. (Old Hillsbrad, CoS, etc)
Step 1: Drink a Noggenfogger so you become a Skeleton.
Step 2: Change into a form.
Not sure if it works with other things instead of Noggenfogger, perhaps someone can see. Works with all forms, including Travel Form. Fast running with that + pack looks weird :P