Joe, it's possible to put a topit into a waist-length coat or a vest (worn open), and I've seen people work successfully with one. Note that it limits the size of objects you can work with, and also will constrain the hand motions you can use.
The choreography of a routine with the topit is critical, and it's best used to clean up a trick (dumping a gimmick the audience doesn't suspect, for example.) It's one of those methods that should be used sparingly, because doing too much stuff with it tends to communicate what's going on to the audience.
The two best references on the topit are from Michael Ammar, who did both a book and tapes, and Carl Cloutier, who did a set of tapes. They take different approaches to the routines you can do with one, but to your point -- they both use a suit coat, not something more casual.