For the most part, voluntary/optional benefit enrollments are handled as general deductions in PeopleSoft. Examples include voluntary life plans and Section 125/Flexible Spending Accounts. General deductions are set up under the Payroll module. Complete directions for setting up or modifying can be found in the Ben Admin guide. Here is a link to that guide: PeopleSoft Benefits Administration (BA1)
Also, remember to set up the deduction overrides for any new general deduction that is set up for an employee.