How to setup Eligibility Rules for Vacation Sell plan

We are setting up Vacation Sell - Plan Type 91 using Ben admin as a separate election cycle post OE, so employees can enroll using self service.

However I don't see any Eligibility Field available as delivered to set the criteria for eligibility of this plan? Staff eligibility would be based upon a specific vacation accrual amount in current year at the time of the staff member’s election.

I am wondering how other organizations are using ben admin eligibility field criteria for this type of plan.