Entry of purchasing invoice

I'm wondering if there is a way to link a purchase invoice to a receipt after the invoice has already been entered. Since the receipt is done using the purchase order, can the invoice be entered using the purchase order and then manually or automatically matched?

Currently, we are holding international invoices (6-8 weeks), waiting until we receive the product, and then linking the invoice to the receipt. We want to pay to get a discount, but cannot do so without entering the invoice through AP/AR Accounting. When the product is received, we must re-enter the invoice to link to the receipt and then do a credit memo to clear the invoice.

Is anyone else running into this issue or is there a work around?