2007 Tiburon Valve Stem Problem

My 2007 Tiburon is the first time I've had a car with a TPMS, and I'm experiencing a bizarre problem: the metal valve stem covers are essentially fused to the valve stems! They are so thight I can't get them off and the local tire place couldn't get them off either! We tried using two wrenches, one to hold the barrel in place and another to rotate the cover, but there's a cylindrical piece in between that rotates with the cover and it can't really be secured. We were afraid of breaking the sensor so we gave up.

I've been soaking the stems with PB Blaster but it hasn't worked so far. The next thing I'm going to try is to briefly blast the cover with a torch to expand it slightly. Any other ideas?? If I ever get them off I am putting a huge dab of ant-seize so this doesn't happen again.

They're not locking valve caps are they? Some valve caps are 2-pieces so one rotates but doesn't undo the threads. I used to have some that needed a little screw to be inserted into the side so you could unscrew the piece that mattered.