I wouldn't recommend wiring it without using a relay. The stock reverse wire circuit is only running a bulb in the range of 10 watts or so. Jumping up to the 55w or so that the dual beam is running will not be kind on the reverse light switch and fuses, and the wires themselves are definitely too small of a gauge. This means you will have to do a run to the battery.
You can use the reverse light wiring to switch a relay though. I did that, as well as installed a switch in the speaker panel. My spotlights come on either in reverse, or if I hit the switch. Mine are also mounted up high on the roof rack, so they make wonderful work lights if I have to help anybody out in the dark.
My oil line fix
My 100k stopped odometer fix
Brace for impact, I'm in a "modifying mood". Massive thread count inbound.