adding heated mirrors

i'm adding heated mirrors to my 318ti and would like to know if there is a way to wire them up to work like a rear diffoger?  they come one once i hit the switch but only stays on for about 3 to 5 minutes.  is there a way to do this instead of having to turn them on and off all the time i want to use them?  and info or diagrams would help a great deal.   thanks

I may be mistaken, but the ones I have done operate just that way. If they didn't I think the elements burn out. If they dont, you should be able to tap the output of the relay driving your rear defoger and run the power off that. Then the defoger times out and kills the relay turning off the mirrors...Tire Proz Stillwater Mn

High End Restyling and Comlete Repair

thanks i'll give that a try.