An old technique before was to open the apu door during decent to allow the cold soaked one to warm up.
After landing and body gear steering was armed F/E just started the APU with no problems.
I don't know of any circuit breakers you could pull to B/S the system into thinking it was on the ground,
Ground safety relay maybe but would lead to many other issues.
Just wonder how much money did they save on fuel by making this apu in flight use impossible now.
Bean counters once again getting into places they don't belong.