you could block up 2 coin slots with plates. Then just  use 1 coin 3 credits slot only , Put a $2 dollar coin mech into that chute ,
One thing though , Do  they make a 2 dollar coin mech,? other might know.  I'm not sure .
 Depends on how much you want to charge you could .
I have been fixing a Williams  ( Jackpot) game with the 3 same german  coin shoots , I'll have a look when i get back to the guys place,and see if there is a way around it , and double check for any  coin adjustment plugs
Each chute has its one relay set up , and one uses a smaller stepper to count up the credits,