You will gain little if any noticeable difference when adding the rear trunk brace to a non type-R. It is a factory frill that is to reinforce the trunk area across the back. Coupled along with the other unique reinforcements provides maximum structural rigidity.
A better idea is to invest in an rear strut tower bar from some company like Spoon, Benan, Mugen or even the OEM /ITR bar. There are plenty of bars available and all sorts of designs and prices to match.
Just to satisfy my curiosity, Why do you want/need a rear strut bar? Do you know what they are designed to do?
Take a look at the diagram to see just what the difference is when comparing the R's chassis and others.
A.