Pre bent line or do it myself?

I'd like to keep my stock rallye's in 5X4, but I'm learning this won't be easy, or even feasible.
If you are assuming that no one makes a 5x4 rear disc kit you might be correct. But more than likely you could have 5x4.5 rotors drilled for 5x4.

Or you could make your own caliper mounting brackets?