Hi mate, i'v just done this on my rs.

Removed all the ABS stuff, used the original rs turbo master cylinder but fitted a non-abs reservoir to it.
I then plumbed the front feed from the master cyl to the T-Piece in the right inner wing, which feeds to the rear left and front right brakes (as looking from the front of the car).
Then the second feed from the master cyl to the T-Piece on the left inner wing.

This still keeps the diagonal split braking system and allows you to keep the rear brake load compensator valves to do their job!

This is how i've done it and it is the best thing I have done to my RS as I now have brakes that work properly!
Hope this helps mate!