Interesting technique. How long is your board leash? I wonder if you could sling the whole thing over your shoulder so as to have both hands free. I'll have to try it as getting the board in and out of its bag is a major PITA.
What someone should invent is a few plastic clips that turns Mongos leash rig into a quick and easy handle. Wouldnt be hard I'm sure. You could just leave the clips on the leash when surfing.