You could get 650c (26") wheels and put them on the bike as long as you don't plan on using any brakes. If you want a front brake, you'd probably have to change the front fork and then you'd have a time trial looking type bike. As for getting a flip flop, any hub for 700c wheels can be built into a 650 rim, the important thing is the number of holes, and the spoke length will be different of course.