You can set up another hourly rate called Banked Hours and select the appropriate taxes to be deducted, then set up another deduction called Banked Amount to enter the net amount of the banked hours to be withheld. It will show up on paystub and continually accrue until the employee wants to be paid out. However it will not carry over into the next calendar year so you will need to make an adjustment on Jan 1  to have the accrued banked amount show up again.