polishing the inside of a butterfly knife handle

Does anybody have a good way to polish the inside of a titanium butterfly knife handle? I haven't got a milling machine, but have most of the other basic tools. If anyone has a good tip I'd appreciate the help.

I'm sure there are better ways, but for my sole butterfly attempt a few years ago, I simply wrapped various grits of paper around slightly thinner, flat files and progressed up to 400 grit, then used slightly oversized felt bobs on my Foredom tool to polish - probably not a perfectly flat, mirror finish, but the same technique could be expanded to work up to 1200 grit paper, followed by less aggressive buffing.