I found this great handle http://www.thingiverse.com/thing:129760 for hex wrenches. However it was for only one size. I've create a customizable version so you can create your own for different size keys.
2.2_Hex_Wrench_Handle.stl | 360.0KB | |
2.8_Hex_Wrench_Handle.stl | 360.3KB | |
4.5_Hex_Wrench_Handle.stl | 346.6KB | |
Hex_Wrench_Handle.scad | 2.1KB |