Accessing absence type DFF from payroll fast formula

Summary:

If an absence type has a DFF for additional information, what is the best way to access that from within a payroll fast formula?

Content (please ensure you mask any confidential information):

I want to enable a DFF field on an absence type to provide additional information about the absence, and for the payroll element fast formula to pick up that DFF and modify the absence payment.

I believe you can use a value set, and potentially use a fast formula type of HR Access for Payroll, but these feel quite clunky workarounds. What is the best way to achieve this?