So to do this is fairly straight forward, but will require adding a relay, running some wires, splicing into factory wiring in a few spots, and installing a switch. I'll have to take some time to go through the FSM for specifics on which wire but I can give you the basic run down now.
If you use a 5 pin relay you can set yourself up so that the factory switch will still work, and the new switch you install will function like an override/bypass to turn the fogs on manually. The only thing I'm not sure about there is the simplest way to physically splice back into the factory relay power path. I know it can be done, just need to figure out the best way.
Anyways, here's the plan. Run a wire from your switch in the cabin to the remote trigger of the relay, with the switch spliced into 12V on ignition on the other end. Ground the relay wherever is convenient near where you place it, that completes the switch circuit.
Run your own 12V power to the relay. If we can easily hijack the run that normally goes to the factory relay this gets easier. You break that circuit (cut the wire) and connect the hot side to the power for the relay. Then you connect the other side to the 5th pin on your relay that is powered when the remote trigger is off. This lets the relay just pass through when it's off and the can functions as stock. Hook up the fogs power directly to your new relays last pin that is powered when the relay is triggered.
I don't believe this is something I could do myself very much anymore. Haha!