How to handle suppliers that submit AP invoices prior to services rendered or milestone reached but

Summary

How to handle suppliers that submit AP invoices prior to services rendered or milestone reached but want to take payment discount

Content

We have some suppliers that consistently submit AP invoices to us prior to services being rendered or project milestone dates being reached.  AP will not pay these invoices until they are received in Oracle (we are setup for receipt accounting and matching on receipt in AP).  The business will not receive the goods/services until services have been rendered or milestones have been reached.  Therefore, the AP invoices go on hold until they are received.  Often the receipt is too late to take the payment discount.  We are looking for suggestions on how best to manage this early AP invoice submission