Prorating Terminated Employee's Deductions

Our long term disability DBA is set up with a table method that calculates Percent of Gross/Basis= Salary. We pay our employees once a month. When an employee is terminated in the middle of the month the DBA only calculates the deduction by the amount the employee earned that month. The problem is that they are still covered for the whole month and we have to pay our insurance company the whole amount no matter how many days they worked that month. I tried setting the rate control to 2 but that did not work. Is there a way to