I would do as +d said... this circuit is in A LOT of RV's, both lighting and pump circuits. For example, to turn the water pump (12V) on or off from the bathroom OR the kitchen. You can even get illuminated (when load is turned on) rocker switches for this.
Assuming you want to use a single wire to trigger this from the Jeep, (like the center lug on a 7-way plug?) you would use a relay for the second "switch". The relay would be like the ones illustrated in HenryJ's post. This relay would still require use of the existing ground circuit. (And the switch in the jeep will not light up when the trailer switch is turned on.)
This is all in addition to the dedicated, fused relay in the secondary (light) circuit. You want to make sure you isolate the wiring so you in no way bypass whatever you use to isolate your starting and aux batteries, too. This will probably not be an issue, but is worth checking.
Another option may be the driving/fog lights that install with a remote control (wireless) switch. Check the Hella site, I think they sell them.
Now I have to go chase electrons in HenryJ's illustration.
Good luck.
Bob