Do you have a valve at the tip to resist movement on pedal return only? If not i think it takes a bit of tubing, a T connector and a adjustable flow restrictor, all available at the local pet store. Bicycle tire valve could work..
But great idea, a must try for me.. I've already modded the hell out of my Momo and want to do more.. Layer of silicone for the cogwheels is my best invention so far to eliminate any gaps, this could come in as a close second.