One of the guys in the Danish 3D DIY facegroup asked for a solution, for his original Ultimaker bed. 

It moves quite easy when not enabled, or when power is disconnected. 
Same problem I have seen online, with the Cetus 3D printer, where a printed part was used. 

My solution is: 

Short out the stepper, when power is disconnected, or the driver is disabled. 
This is done using a regular DPDT relay, and (if you're using drivers with !ENABLE) a MOSFET/Transistor. 
I'm working on a schematic for most uses, and also a PCB. 

But the fun thing is in the relay: 

When the coil is energized, the stepper lines go through the relay, to the output. 
When power is disconnected, the relay goes back to NC, and shortens the stepper. 

I just need to work on the driver-circuit for this, so the enable stuff will work. 

Have a nice one!