20 minute power off auto delay

The last vehicle I owned had a 20 minute power kill if I left the inside lights on which I did on several occasions. I am befuddled why Toyota would not put an auto power down on the prius. I have read many threads on P.C. about people having dead batteries.

Soooooooooo.....

I am willing to do this mod and post the "how to" with pics. Can some one tell me what relay or wires I need to trip to kill the power to the inside lights? Is there a way to kill all power except whats needed to operate and enter the car?