Add a second CIM mirrored across the center of the gearbox from the other CIM with a pinion on the second CIM
http://store.andymark.biz/am-0034.html
According to the Andymark Website all the hardware to attach two motors is included
Check out the instructions
http://lib.store.yahoo.net/lib/yhst-...user-guide.pdf
If you place all the hardware (pinion retaining rings etc on the CIM in the beginning instructions, it shows you how to attach it without taking apart the box on page 12.