At the end of the Nova Mini Maker Faire, I had to stop a print. I was able to resume that print a week later (after unplugging the printer and transporting it in the trunk of my car). Here's what I did with the MakerGear M2 and Simplify3D.
The MakerGear M2's Z-Endstop is set by a bolt on the side of the machine, which gives me some "hackability" when homing my Z Axis.
Simplify3D lets you set up the Starting Point of the print which gives me the ability to tell it what height I want to resume printing at.
Your mileage may vary, but maybe some of the techniques or concepts will translate over to your printer and/or slicer!
My full GCode changes can be found in my accompanying blog post at: http://tgaw.com/wp/?p=375