Purchase Add Ons Online (recurring fees)

Since the system only allows you to have ONE membership at a time, is it possible to enhance the RECURRING FEES feature or copy it and call it ADD ONS that we can sell online?

Scenario: A Member wants to also pay for a monthly locker rental (recurring 1x a month fee). And, I have another Member who wants to rent a locker just for the month of December.

I'd like them to be able to purchase this add on online from a section of the portal, just like they would a package and give them the opportunity to select the start date and select whether it is a one time payment or recurring monthly fee.