If you mean adapt the front 4 piston calipers for use on the rear brakes after upgrading the front brakes with something larger then you're going to at least need a custom rotor and mounting bracket. The rear rotors at 18mm are not nearly thick enough for the front 30mm caliper to grab a hold of properly. You'll also need to incorporate the parking brake drum feature of the rear rotors into the new rotor.
But if you could do it then it would be a good option for the money compared to a $2000 rear brake kit.