Actually the Roland system would still respond to played input... At least I seem to remember that. Basically, to be able to use the LWR area to play on while the CS played uninterrupted, all you need to do is go from LWR1 to LWR2 and the MIDI channel should change, avoiding the chord recognition, or set the arranger to respond to NTA only.

TBH, most of the time you use the CS, it's for doing far more expressive lead sounds with a lot of bender use, or another instrument or keyboard, so confusing your arranger with unwanted notes isn't a huge issue.