There apparently are big systems with electric/spring brakes. . . when the system is de-energised, the springs apply brakes to fight the gravity that never de-energises. :)

like a Stepper Motor with electromagnetic break? I think I have seen that on Servos.

Another thought I had why the PK296A2A-SG18 would be good is when the Gecko drops to 70% the torque... recirculating.

If one could attach an electromagnetic break to the PK296A2A-SG18 that would be a good solution, I guess.

This thread then drifted to other counterbalance methods:
http://www.mechmate.com/forums/showthread.php?t=1026