How do you setup 2 deduction amounts for Domestic Partners (Pre-Tax & Post-Tax)?

We need to set up a Domestic Partner Plan Option for Medical, Dental & Vision. How can I split the employee's deduction amounts to be Pre-Tax and Post-Tax)?

I had setup up the Benefit Plan used both the Employee DBA ID (FDBA) field & the EE Flex Credit (PDDP). The Employee DBA ID (FDBA) field has the Pre-Tax deduction DBA code and the EE Flex Credit (PDDP) field has the Post-Tax amount.

When I enrolled the employee in the Benefit Plan option, the deduction amount only showed the amount in the Employee DBA ID (FDBA) field but not the EE Flex Credit (PDDP) field.