Yes, CTRL+Shift+F1 should work, GSX reads the standard FSX variable for the RPM to know if an engine is running, since the Q400 has its own flight model and engine simulation which runs externally from FSX, it's likely its own engine parameters won't match the FSX ones, but the CTRL+Shift+F1 key is still working and acting on the standard FSX engine simulation, and this should made GSX happy.