It looks like you could do this with the L-Pol/R option in the Stereo Image settings (Processing>Preamp) for the stereo pair. What you don’t get is an L/R-Pol option, although you can invert the right channel if you don’t mind also flipping the two channels (R-Pol/L). I haven’t actually tried this on the console, but SQ Mix Pad seems to indicate that it’s possible.
Instead of making a stereo pair, you can always gang two (or more) channels, but then the input gains don’t track.
Never mind. I thought I was looking at the SQ forum.
Geoff