Summary

OK.. too busy to do that automatic version, so here is a clamp design to do the same thing manually I hope.
set you Z just above the bed (say 1mm), loosen all four clamps (stl's coming soon, 2 as the one shown, two mirrored)
Move to first corner, lower it 3 mm or so and tighten the clamp for that corner, repeat for all four corners, set extruder z height at that height for your zero...

This is specific for the Makerfront prusa i3 steel.

You should need one M3 screw and two M3 nuts for each clamp.

Update 2 01-31-2016
Finally came up with a KISS solution, dumping the servo and just making clamps with knobs for each corner. Will make a simple macro for pushing the bed down in each corner, hand tighten the knob, repeat for each corner. Once I get my cheap Chinese extruder working I will test out some designs and post the final design.

Update 1 01-02-2016
Happy New Years..
Modeled in the servo mounts, shortened the clamp and wedge mechanism.. slide rails now two part to most printers can fit the print on the bed.

Still may need a major redesign to clear the back of the printer frame..
CADing up a model of the printer, should make it easier.

More to come.

Doing a press to level where the nozzle pushes the bed and the posts are clamped with a servo. This is the clamp mechanism. Need to add servos and mounting system, etc.. just a rough start. Not ready for downloading and printing, just wanted to get what I had so far up here.