Short version: Using the standard New Custom Field Set form, it is currently not possible to create a multiple-record field set for memberships. Is there some other way to achieve this?
Long version: I work for a membership-based society comprised of, among other things, a number of choral music organizations. As part of their being members, we would like them to tell us the names of the choirs that are part of their organization, and the number of singers in each choir. Given that a single organization can run multiple choirs, a multiple-record field set would be perfect for this information...if only I could create one. Using CiviCRM's built-in facilities, the only options I can see available to me are:
a) creating a finite series of separate fields for the membership type based on some reasonably safe assumptions about the maximum number of choirs a single organization is likely to have, or
b) creating a new contact type specific to these members, creating a multiple-record field set to associate with it, and then forcing someone in the office to update the information manually.
At present I'm leaning toward the first option, but I'd love to hear if anyone has any other ideas, especially ones that would allow me to use the correct (for the situation) field set type associated with the membership scope.