There are a lot of cautions and warnings in this article! FIRST: I am not responsible if you destroy something attempting this modification!
**I highly recommend using the EXACT same MODEL/HP motors. I suspect if you don't, you're likely going to destroy/burn up something.
**I know this works with KBAC VFDs.... I would not recommend trying it with any of the el-cheapo VFDs! You'll likely end up in a Blaze of Glory.....literally!
http://www.caffreyknives.net/1_vfd_2_motors.html