There is a simple measure that can work and it is not a shot clock. All you need is a time limit for a given match. A race to 9 should take around 90 minutes, for example. Should the time expire and no player has reached 9 games, then the match is over and the player with the most games wins. If there is a tie, then let them play a 1 game tiebreaker with a time limit of 15 minutes. Without a shot clock the players will not feel rushed, but they will be aware that the time limit is also a factor.
That would not work well, in a slow match with a player having a 3 game lead or so that player could purposely slow down play so that the time limit expires and he wins without needing to get to 9.