The Schlumpf is an interesting choice for internal gearing on a bike. I've looked at them for doing a 2spd with a chain and single cog on the back. I'm pretty sure they only offer 2 ratios, not 3 - so it gives you twice as many options as your current drive train - so a 9 cogged rear on a bike would yield 18 'speed' options. For a mortiser you'd have 1:1 and then lower or higher depending on what option you chose (unless you also somehow had gears right @ the bit spindle.
The Schlumpf works by hitting the center 'button' with your heel as you come round on your pedal stroke. They make a 'mountain' drive and a 'speed' drive (essentially one that works to lower your gearing (for touring) and another that would higher it for flat / road riding.
There are gear ratios and such posted here:
http://www.schlumpf.ch/sd_engl_funktion.htmhttp://www.schlumpf.ch/md_engl_funktion.htmAnd pics of the internals here:
http://www.schlumpf.ch/sd_engl.htm 
The issue I'd see adapting this to a boring machine would be running a short chain or developing a gear cluster that turned from perpendicular to horizontal to drive the bit. Not impossible - but a typical bicycle bottom bracket (which houses the unit) is 68 or 73mm wide - so you might have to make the spindles / axles that carry the arms (or cranks, in this case) longer. The assembly would have to sit in a properly machined and threaded shell.
You could buy an adjustable one
here. Or a blank that would require fabricating / welding / brazing it to other components (maybe the internal frame that moved up and down...)
here. I see a short chain drive turning a cog on an axle that then is geared to turn a bit. You'd have to build a rigid stand for it, and work out the geometry such that with all the hardware it wasn't too tall or wide while sitting on a timber. Could be a cool project. I'm already envisioning how the drive system could work with an axle and gearing to change the direction on the bit. And then maybe have a ladder that the whole rig climbed to help pull it out of the bore hole. Machined aluminum maybe for the framework.
When I planned to cut a frame for a friend back in 2003-2004 I schemed up all sorts of bike related mortising machines and routers. Would love to have 2 setup - 1 for boring mortises, another with a 2" forstner type setup for roughing out housings... something I never investigated fully was how to get around the chain / interface part - but if Tim is gutting car parts and getting gears to work - it would seem like something that is possible...
