Restrict Invoice generation on award contracts

Summary:

Looking for the best way to avoid invoice generation on certain award contracts (billable project type)

Content (please ensure you mask any confidential information):

Our client has a requirement not to bill for certain use cases (example: a project is fully funded by an internal funding, we need to create an award for tracking purpose. The projects created under non-billable project type are not available in Grants, so we have to create billable projects even though we don't want to bill). Using Internal funding functionality within the award doesn't seem to work well either, since the system requires (external) funding source i.e a customer for any award and the funding allocation must be done for both, external source and internal.