Once I figure out how to post pictures, I will, but this will answer the how I did it.
Ingredients: 1 35 dollar black SF G2 Nitrolon, 1 50 dollar DD offset mount, 1 GG&G rail mount swivel. Last two items picked up at Lightfighter's retail store while on lunch break today.
Mount Nitrolon in DD mount for LEFT side use, rear of mount ring even with start of tailcap threads.
Mount DD mount to issue KAC rail, far enough back the M203 breech latch is accessible between the shaft of the light and the latch.
Mount GG&G swivel to L side rail aft of light, shorten the already in use CQB Solutions 3-point sling to accomodate shorter reach to swivel.
Very easy to work light with thumb of left hand while supporting weapon, very fast reload of M203 as the light doesn't block the latch, in fact the light-forearm gap helps guide the tumb right to it. Also no risk of swivel binding the latch as happens with the stock GI barrel-mounted side swivel.
A happy ending. Total assembly time, maybe 20 minutes.