How much modification are you interested in doing?
You will have to change the door switch to high side switching instead of low side switching. If you don't already have door switches, you can get normally-open 2 terminal ones fairly easily.
If you want to make that change, do you want the lights to come on when the door is open OR the current switch is on? Or do you want them to come on when the door is open AND the current switch is on?
In the latter case, the existing switch acts as an override for the door switch.
If you like, I can draw you some schematics for how to set this up.
