Why wouldn't setting the selmode to 0 work? If you still wanted it to be selected for some reason, but not visually represented, you could set its color. If neither of these work for you, maybe an explanation of your end goal would help us help you.
My jit.cellblock cells are all different colours to correspond to the colours represented on my Novation Launchpad, the colours changed depending on it's mode of use. The selection cell therefore shows up a different colour on the screen than it does on the launchpad. It is a minor irk but perhaps could be a distraction in a performance situation.