Hi Gary,
Have only just seen your question re X55 . I have done the reverse engine on one of the toggle switches . In control settings in FSX ..Rhino throttle .. button/keys , I assigned a toggle switch to be F2 Throttle (decrease quickly....reverse engines) to the forward position (you need to hold the switch forward to get full reverse) ..Then assigned the back position of the same toggle switch to F1 Throttle (cut) to stop reverse engine.
Many other functions can be assigned to the switches easily.
Brian