At the OWC, the best place to do it is in the front, almost right after you pass the booth and before the first tabletop. That's also the case at the Texas Ski Ranch.
Practicing them on the cable is like doing an air backroll behind a boat. You cut and load the line, then bring your shoulders forward with the release. Release forward and re-direct the forward release to the right with your shoulders. The key is to get the release forward first before you slip, otherwise you will spin flat instead of inverted. I haven't landed any of these yet,but practiced them a lot in the beginning when I was first learning a backroll.