create a wordpress-plugin,
which scans a google calendar for certain entries, e.g. "open", and builds sellable/bookable "service hours" (products) for each hour (or any other timeslot, such as 45 minutes) for all future entries. Removes not-booked service-hours if they are no more within such "opening-hours".
Background: a therapist with very irregular opening hours wants to sell single service-hours using a common webshop and maintain everything with his google calendar.