Well the pedals can be freed off but it's highly, highly doubtful that the master cylinders are usable in their current state.
If you're determined you could probably get them repaired by using a stainless steel sleeve to repair the pitted bore, it's used on classic cars etc where new cylinders aren't readily available, but may not be cheap.
The brakes can be used to steer the machine, there is a declutch control valve you can set which disengages the clutch when you press the brake pedal should you wish to use it this way.
However, I found that since the original master cylinders are so knackered and awkward to access it wasn't worth the bother. Yes you can turn sharper with the brakes which is quite nice in a tight spot but for 98% of the time I found it unnecessary, and so I ended up fitting a car brake cylinder instead which goes to both brakes together which is used purely to stop/hold the machine when working on a hill. That's the only time that I've found a real need for the brakes.