Yeah, I ended up doing that. Select all > unselect all the files I didn't want converted > convert > hope to hell I don't accidentally unselect the original files as they convert > right click and delete. Only one problem, and it's a very small one, is that all of the actual music files in my library now have a 1 at the end.
I'm still interested in finding a better way to accomplish this. If my library had been bigger (I have about 1,000 songs) or more non-music files mixed in my library it would have been a much less practical solution.