USGCO

I am a CO for the USG. I have a big contractor that does not like to submit invoices on our FFP contracts until delivery. My customer would like to have regular invoicing, and has requested we hold the contractor to a "spend plan". My contract includes the Progress Payments clause, but my understanding is that we can't force the contractor to submit progress payments if they don't want/need to. Someone please tell me I'm wrong. Can I add a payment schedule to the contract and enforce regular billing on my contractor?