I've got the same system with the same problem.
Here's a pic of how I solved it;
Used the safety tool that came with the system, attached to the piece of aluminum, it will reach the inner valve to remove the sensor & using a rubber band to hold it in the tool will allow you to thread it back on, so far its worked for me.
If the tire guys mount the stems directly across from each other it's a little more difficult, but if mounted 180 degrees it works good.
One plus for me is Discount Tire scratched the crap out of both front factory wheels ($808 each from GM dealer) so they replaced them with 4 beautiful aftermarket wheels & now outer rears the valve is in the outside.
I've never found extensions that I thought were worth the $$$ & do what I want.
Hope this helps.