UPDATE ON 2015-11-20!!
Dale Jordan of Oregon FTC made a number of enhancements to the original designs. He added slots for the zipties to slide under, he made the ziptie holes rectangles instead of circles, and he created a very nice mashup of the original power module strain reliever and the strain reliever at this link: http://www.thingiverse.com/thing:1096699. All files that start with DJ_ are his. Feel free to download the whole set and use what works best for your robot design. These files are posted here with Dale's permission.
Thanks Dale, and thanks to VCHS and Matt Rain for the original thing 1096699!
V5: includes ziptie "cutouts" so the mounts can be mounted flat on a plate without having to cut extra holes in the plate for the ziptie to run through the plate. Thanks to Dale Jordan of FTC Oregon for first introducing me to this idea through his enhanced designs.
Later version #s: adjusting hole spacing a little closer for slightly tighter zipties.
Strain relief for the small USB connectors on the various Modern Robotics modules being used on FTC robots.
Print flat. Then flip the print upside-down on the module to mount it. Screw the module plus strain reliever to your hardware using the normal screw holes, and secure the usb connector with a small ziptie, similar to what was done with Samantha module strain relievers in previous years.