If there is no salary to deduct from, you can deduct outstanding costs when there is salary to deduct from again. Alternatively, you make advance deductions from the salary if you know that an employee is, for example, on leave for e.g. a number of months. In this way, the agreement can continue as usual without you as the employer suffering any financial loss.
An alternative to gross salary deductions as above is for you to invoice the leasing fees to the employee as a regular invoice for his leasing costs.