How to send a Books invoice to the Contact Roles of a Deal?

How to send a Books invoice to the Contact Roles of a Deal?

Hi

In our implementation of CRM we dont use the Accounts module, we only have the Contacts and Deals modules. Each Deal will have 2 Contact Roles (the 2 roles are obviously 2 separate Contacts).

Now we have integrated Books and have a 2-way sync between Books and CRM. 

Is there a way we can send an invoice from within Books to both Contact Roles of a Deal? Im pretty sure we can do this if we create an Accounts module in CRM and apply both Contacts to that Account; then sync the Account module to Books. However, this would involve a lot of reworking of CRM custom functions, blueprints, workflows etc. 

So is there a way to - without using the Accounts module - send an invoice to both Contact Roles of a Deal from with Books? Possibly by using custom fields?

Thanks