You can use a thick piece of leather and a good vise to hold it, or better yet - a thicker strip of brass that is thin enough to bend around the brass piece and use vise grips to lock down the brass end. With that end secured you can wrap another piece of leather around the barrel and use vise grips just snug enough to let you gently twist and work it out.
As far as materials acquisition - use an old belt or buy one at a second hand store (you can usually find "real" leather belts at those stores). They sell brass strips for a few $ at most hardware stores.
The barrels are thin, so use caution.
EDIT: if you're trying to separate the brass TP piece from the stainless piece, you'll also (likely) need a propane torch. See this for the process to separate:
https://m.youtube.com/watch?v=TjDZFikC7MI