Car amp install without re-wiring?

Well here's the situation. My friend has a leased car (mazda 3) and he wants to put in a removeable sub that he can take out when the lease term is over. Now buddy here doesn't want to do all the technical wiring so he's planning to have a sub in his trunk and then using the factory speakers for his highs and mids (whatever isn't bass). How he plans on doing this is that he has an ipod which he uses for music that he hooks up through the auxillary jack, so instead of only going to the car stereo, he has a y-adapter with a male to 2 female 3.5mm jacks. That means one side will go to factory speakers and one to the sub only. The problem now is how can we hook up the amp. Is there any way he could get a adapter for the car cig lighter thing to get power to the amp?