Earning Elements need to be used for Rate calculation

Currently we have one of the earning elements entered manually and processed in payroll. Client medical rates are salary band rates and we need to include this earning element along with annual salary for the rate calculation. Typically the value can be changed or end dated anytime during the year, which should re-calculate the rates.

Can we refer value from elements for rate calculation in fast formula. If yes, provide some insight on the design.

If there is any alternate way on this design (other than holding the value in benefit balance/in flex field), please let me know. Thanks in advance!