Hmmm... I've seen those on a buddies KTM and he swears by it. Much better control of the rear brake off road, especially when standing.
The hard part of this idea is that the brake isn't hydraulic. But... just thinking aloud here... if you welded a stay onto the swing arm tall enough to be at the same height as the current brake rod, you could remove the brake rod and hook up a cable to the brake arm, then insert the housing of the cable into this newly welded stay, and then attach the other end of the housing into a handle bar mounted shorty lever. This idea would require losing the current setup.
If you wanted to keep the pedal active and ADD the handlebar mounted lever.... you could weld on an extension to the existing brake pedal on the other side of the pivot point, then use a cable system to pull up on this extension to simulate the downward motion of the pedal. Making it all tight against the frame and out of the way of your feet will be tricky, but it could work pretty well if executed properly.