I do not have an answer for you but think it's an interesting issue. The belt clip part makes it interesting. I just use a zip lock sandwich bag that I stuff a tube, patch kit, tire iron, rubber gloves and 15mm stubby wrench wrench and hide it all under my brooks saddle with a Christophe strap laced through the rear eyelets and through the saddle rails. Works like a charm and almost totally "hidden". I've seen dedicated saddle bags of course but never really considered purchasing one. I like your thinking, though.