I had a similar adventure with my '72 cutlass - 18" wheels with C6 z51 brakes and soft lip rims. It's cozy in there.
I banded TPMS sensors into the drop. Works fine. One of the guys at the tire shop didn't want to touch it, another guy was fine with it. Took them a little while longer than normal, but those are custom polished aluminum rims, so extra time is warranted. 
Band the sensor next to the valve stem hole. The low profile stems weigh almost nothing, so having the TPMS sensor where it normally is will help the tech balance the wheel like they normally do.
I also bought my own right angle low profile valve stems off amazon. They work fine. I was able to use shorties on the rear. All of them are a major PITA to use when the wheel is on the car.
Granted, the Firestone guys know me. The shop is a 1/2 mile from my house, so I just take everything there for tires and alignment.