I would like to be able to mark cells that won't get any more dice. Sometimes, when I am assigned an opening configuration with cells all over the board, I will manage to get four connected on one side of the board, only to see most of my four dice get allotted to a cell across the board that I have already written off.

This wouldn't take additional time in game play, as we could mark the cells while waiting for our turn. I don't know whether other players should be able to see which cells you are conceding.