Interunit Billing for Grants

Hello,

We are looking for some information on the following question:

When Customer is flagged as Interunit customer, it cannot be selected on the Grants proposal which leads me to the conclusion that no standard award/contract can be generated. How should we proceed if BU 'A ' gave a memo/funds (sort of sub-agreement) to BU 'B' ? Should we proceed w/o proposal but just creating an internal contract and then go backward creating an award (sort of blue bird award)? If that's the case, would we be able to use the contract for generating the interbill? We don't want to use Billing for creating invoices online.