Well, never done this particular thing before, but have played around quite a bit with remote glow drivers and other switched items which work off the RX signal. I would think if you had a RC controlled switch for lights, you could just Y it with the pump on the same channel just like you woudl with two servos. Then you adjust the lights to come on the same time as the pump and you are good to go.

To get a better feel for how something like this works, take a look at the [link=http://www.cliftech.com/html/optoglo.html]Optoglo II[/link]. Going through the documentation on this will help you understand how the system (smoke or lights) can be made to work off the RX signal and how the adjustment works. If you get really ambitious, you can build an Optoglo yourself and use it as your light switch. After a few failed attempts with substitute parts, I finally got one to work by ordering the exact components as listed.

Duke