I have been considering trying one of the cheap Chinese TIG pedals off ebay for a while, but not got around to pulling the trigger. They have a potentiometer in which is turned by pedal movement and it "should" be able to control a VFD. I am pretty sure the one on my cheap Chinese TIG welder has a microswitch in there as well which switches at the start of the pedal travel. Mine has a single multipole connector, but there are others listed on ebay with a 3-pole and a 2-pole connector, suggesting a microswitch and a potentiometer. It has been reasonably ok on the welder, but something internally has stuck on a couple of occassions, requiring percussive maintenance. It has not yet reached the stage where I have needed to open it up.
Some of the KB drives might not be as easy to set up for this as drives from other sources: the KBAC hybrid drives certainly seem to be designed for easy setup by a "normal" person in 90+ percent of applications. I get the impression that the downside to this is that they may be less flexible for the tiny minority of "odd" applications. Do you have the part number for the drive?