If I understand you correctly, I would tap into the wires at the light - through the wall - to the switch. And from the nozzles - through the wall - and also to the switch. Power could be turned on an off to the nozzles as long as the parking lights were on I think.

I looked at the firewall but couldn't see an easy place to sneak the wires through. All of the spaces I see that wires go through are put through rubber grommets and that plastic stuff (wire loom I think it's called?). Any suggestions?

By the way, it's the '91 CRX firewall, not that I think it's changed much from the '90.