Out of curiosity--Say I found a super-sweet rigid mountain bike frame (Trek 950) that is really large (22"), and not so good for me for trails due to standover, but is sized and angled pretty perfectly for a cross bike and has enough clearance for 700c wheels and knobbies, is there an inexpensive workaround that would let me swap in 700c for 650s? Like some sort of extreme-range cantilever brake or a brake bridge with bosses?