Buffer on SGPRS


I need to create a constant buffer of 256 uints on SGPRS. The goal is to increase the access speed compared to LDS. When the kernel starts it first creates the buffer on LDS and then I use it. I think if somehow I could create the same buffer on SGPRS (I think we have 512 SGPRS per SIMD) the access speed would increase. Right? The problem is - how to do it?