Its not always necessarry to spend a wedge of cash everytime you want to change something on a GS guys...
There is a small adjuster stop screw which for the price of a small spanner can be adjusted to set the pedal higher or lower.
Two 10mm and one 8mm will do the trick
I'm not certain its as simple as that (well I dodnt try but was advised it wasnt straightforward), that screw is the brake switch actuation adjuster isnt it?
It's as simple as that

Except that there are two screws to adjust.
I just did this to my 1200gs today (only been meaning to do it for the last two years).
Very straight forward, screw the front one down and the rear one up.
Be carful not to over adjust the rear one, as it will mean the pads will be rubbing on the disk. The front screw needs to be adjusted so it realeses the servo/brakelight switch almost as soon as your foot touches it.
Finaly three important things:
Recheck the rear pad clearance after about 50-100 miles.
Don't forget to tighten the locking nuts.
If your not sure what your doing DON'T do it 'seek help'
Returning to the reason for the thread in the first place.
Even having done this little mod, it's unlikely to bring the brake peddle up high enough for ease of use off road
As has been suggested already, fitting some kind of raised platform will prove to be more of an advantage. (an esily removable one,even more so)
Val.