Unfortunately that won't work. If you were using a purely digital device, just off and on, then a relay would work fine. But your dealing with an analog device that varies the output to produce a dimming & brightening effect, not just off and on. A circuit could be built using a triac or similar components but I think you'd be getting in over your head. Two 500watt lights are pretty impressive as is. That alone will pull over 8 amps. I suggest trying out what you have and see if you like it.