Generating Revenue Commitment Reversals

I have a customer for whom I have setup Revenue Commitments. They use classic Rev Rec, not ARM. They need to recognise revenue separately from billing, so they are generating revenue commitments. Integration from SFDC feeds Sales Orders into NS; they then manually create the Revenue Commitment and the rev rec schedules, and at some point later, separately, they start billing. They do not use Inventory, and their non-inventory items are not marked 'can be received or fulfilled' - they do not need any fulfilment step.

The question I have is how am I supposed to reverse Rev Rec if the Sales Order gets cancelled before billing? Because items are not marked for fulfilling/receiving, the Pending Billing and Revenue Committed Sales Order does not have a Return Authorisation button available. The Revenue Commitment transaction does not have a 'generate Revenue Commitment Reversal' button either. I enabled