Usually to attach anything to a roof involves drilling holes and putting screws in, then there's the hole for the wiring... I wouldn't mess with it on a rental house.
You CAN save a lot by switching to LED bulbs, I posted about the Cree 60 watt equiv bulbs I bought, they use 9-1/2 watts each, check out my post on them in another thread in the "off topic" folder:
You CAN take those when you leave! they are even more efficient than CFL bulbs, I'm getting rid of all of my CFL's and changing over to these LEDs