I wouldn't.
I test drove a BMW Z4 Coupe with Rainsports on and was sliding all over the place.
Ok, it was raining and the car has 265bhp, but that's only 30bhp more than my Z3 Coupe and it takes a damn sight more right foot to get the back out in the wet with my Michelin PilotSports.
I think i'll just save and get a couple of contisports to match my rears then. They were fantastic when on the front.