Need to create series (like a conference) with custom record -suggestions?

I have created custom records to manage my client's workshops (standard events was not going to work).  There's a workshop record, a workshop attendee record, and evaluations.  The workshops are tied to Items from accounting to report on # workshops for each item/type, as well as for invoicing the customers.

For most situations, this is working beautifully.  However, there are two instances where it isn't -- one is a module in which 10 workshops make up 1 module; and then 4 modules are required to be completed before the customer will receive their certificate of completion.  Outside of using Item Kits or Groups, is there a way to tie these together AND maintain that the attendee is only paying for the module and not each of the 10 workshops?  At the same time, they are offering a discount to complete all 4 modules, so this needs to be reflected in