Main issue you will come across is how the boot fits into the baseplate. Most pairs of mediums I have seen the straps fit up to a 10.5 boot fairly easy but once you start gaining width to the boot is the main issue. Getting new straps might buy you a little time.
For some reason I have a feeling the straps are the same from large and medium( I know a lot of their parts fit both but I have to double check that for the straps). I know the highbacks are the same size whether you have mediums or large bindings.
Edit This just pertains to Flux Bindings