There is definitively a better way to approach this, yet it would require substantial changes to the existing top and sub model. A detailed understanding of table Schemas and repeat groups will set you on the right path.
As a quick work around, yo want an Object Reference property of Type Object placed within your submodel. In the main model, you need to place the name of the Secondary Resource which it may use. Send me your email in PM then we can do a quick screen share and I can show you if you dont come right.