Towards the end of the thread...namely the KC diagram. CLICK:
aux reverse light question
This allows for a: when you put trans in reverse, the aux lights also light up with your taillight mounted reverse lamps and b: when you flip your dash mounted switch, the aux lights light up (independent of what the transmission is doing).
Or as posted above, wire in a new circuit for the new lights and use your reverse gear wire to trigger the relay. Meaning they'll only come on when you put trans in reverse. The KC diagram linked above also covers this type of wiring too.