I believe you are referring to the BAG motor, correct?:
http://www.vexrobotics.com/217-3351.html
If so, the best way we have made use of all the smaller shaft motors in the past is to put them in a Vexpro versaplanetary gearbox. You have many output and gearing options at that point. The gearbox comes with the mounting kit and collars to use pretty much all of the legal motors.
http://www.vexrobotics.com/vexpro/mo...planetary.html
You can assemble them with 8mm (CIM) output shafts, 1/2" hex, 1/2" round, 3/8" hex etc. Just make sure you order all the parts you need including the ring gear kit per stage if you're adding stages - and lubricate the stages with white lithium grease.