Sure you could. You'd just need to write a ASCOM driver that called the correct commands. Make sure you set that it is an absolute focuser even though it isn't. Most Astro focusing programs can't handle non repeatable focusers.
If you do, would you do it for Nikons too?
Some cameras such as the D7000 and D800 have the motors located in the camera body and can focus via the SDK. I'm pretty sure Canon offers the same feature. qDSLRDASHBOARD allows me to do this. It's pretty slick; I turn live view on, find a bright star, and just watch the star as I 'focus' using push buttons on the screen of my iphone. If I remember correctly, BackyardEOS allows this feature (manually) but he never added it to BackyardNikon.
The guys I've seen that use a belt to the lens body usually use a stepper motor and have that attached to a program that counts steps. My FCUSB was able to toggle between pretending to be a 'absolute' focuser and a 'relative' focuser. Obviously it was susceptible to slipping, but it worked pretty well. That's what you'd gain if you wrote a ASCOM driver that tied into the Canon/Nikon SDK and used those manual motor controls.