One trick people have used for masts when the next thing is an end of track buffer is a signal that only has stop enabled. Then whatever points at it would figure approach at best.
For your case of manual signals, without Logix to drive them, you'd need the mast logic and it deals with mast pairs. Think of the sensors like the sensors in the signal head logic, any active sets stop. Clicking on a mast will cycle through the enabled aspects.
