invoicing in marketpress

Anyway you could add a function that creates an invoice function in marketpress? Ideally, it would create an invoice product that is private (does not show up in the product list) unless I click a box that creates a random URL to the invoice to pay that I could email to the client for payment within marketpress. I use WP Invoice but it causes issues because the payment integration for PayPal doesn't allow the use of credit cards - it forces you to create/use a paypal account, unlike marketpress! Also, if I want to use a true credit card processor, if I set up two between marketpress and WP Invoice, I'd have to create two separate credit card processing accounts = double the fees. I'd much rather have MarketPress do all this work. Please make this enhancement!!!