How to generate COGS when using third party billing application

Summary:

We have a requirement on our project to intergrate a third party billing application to the Sales Order process.

Our current process is:
Sales Order Issue (Ship goods) > SO moves to 'Awaiting Billing' > SO details sent to 3rd party for processing > Interface comes back to Fusion AR

Problem:
Because we are not creating the Fusion AR invoice from OM using 'Import Autoinvoice' there is no link between the SO and AR Invoice. As such, we have accounting entries stuck in deferred COGS. We need the revenue recognition to be linked so that COGS can be created.

What options would be available to handle this scenario? We still want to utilise deferred COGS.