Well, it could be possible, but not sure, if worth it. I can see 3 problems:
1) When you only highlight a cube, it's still seen as not voted for other players, so some cubes, which you have already checked, might be unnecessary rechecked by other players and if they SC one of your highlighted cubes, the vote goes to them, not you.
2) The system doesn't allow to upvote/downvote a random bunch of cubes. The only possibilities are: a single cube, a cube and its ancestors, a cube and its descendants. So, trying to convert all highlighted cubes into voted would result in a series of requests (sometimes, quite long series, since each cube would have to be voted in a separate request) and could take quite a while.
3) If you'd check and then highlight a cube and its descendants, then the script would have to remember each and every cube in that branch and then send a request for each of them separately, which would take much longer then the current SC+children. The reason for that, is because between your highlighting and your converting to SC a branch might have been grown further down so we can't say, that you have checked the whole branch, but only from a cube to one of its descendants (which was, at that time, the last of the children, but doesn't have to be the last right now).
So, I think, the easier way would be to check a whole branch then SC+children it.