Prevent Billing schedules to bill based on certain conditions (not using Bill Hold)

Summary:

While Bill hold is a standard feature, there are circumstances where you need to prevent a particular billing schedule from billing, based on certain criteria.

Content (required):

Billing a schedule (period) is based on PO# being made available for that period. Since as a standard feature PO can be stamped at line and not at Bill schedule, we could introduce a PO# at the Bill schedule level. We would like to hold off the billing for that schedule if the PO# is not set for that record.

How can this be achieved?

Version (include the version you are using, if applicable):