simple register combiner question

sorry for posting such a simple question - the documentation for register combiners did not yield the secrets i need…

texture unit 0 is a normal 2D/3D texture fetch
texture unit 1 is AR dependent on unit 0, producing R1G1B1A1
texture unit 2 is GB dependent on unit 0, producing R2G2B2A2

i want the final RGBA color to be the AR from the stage 1 fetch, and the GB from the stage 2 fetch.

i.e. R1G2B2A1 -> RGBA

i know there might be a way to do this with RC1.0 using .rgb swizzle notation, but what is the equivalent glFinalCombinerInputNV function call?