Scott, I did mine slightly differently. I went ahead and stored a full registration in each of the 8 memories. Then in the Freeze Parameters, I "froze" everything except the sounds. Of course I put a different sound setup in each of the 8 locations. Now, when the freeze light is on, selecting the registrations changes only the voice. When the lights is off, I have 8 complete setups.
In effect, this gets double use from the registrations.
Regarding your problem with the left hand sounds, you might adjust this method so that calling up, say, reg. #1 would open a 6/8 ballad style with left hand piano, and two right hand sounds. Then hit the freeze button and you could change to any of the other 7 sounds for right hand. You might play with this idea to see if it helps.
DonM