"Time based action" workaround

"Time based action" workaround

I want to create a Workflow Rule that emails a user when a potential's closing date has passed, asking them to update the potential (or close it if they forgot).  Unfortunately time-based actions are only available in Enterprise edition.

Anyone know of a workaround for this, for users of other editions?  We're on the Professional edition and it doesn't make sense for us to ~double our rate for this one feature.

Thanks.