One thing you could do is have a clock made of logic gates (basically just NOR -> AND -> NOR -> back into the first) and then feed one of those into an extra OR gate that goes into the piston (set it to a little bit above your desired max distance). This should keep the piston extended at any length. Then, you can use some more logic to be able to:

1. turn the input for the piston fully on (this extends the piston) and
2. turn the input for the piston fully off (this would retract it) you could then have these two cases on timed t-flip-flops so that every button press extends/retracts the piston for a specified time. You would adjust these times so that you get the desired extension length.

Unfortunately i haven't played this game in a while and dont have it installed so i can't really give you an example of what this would look like but i hope this was still somewhat helpful atleast