Making the Payment Method mandatory at the Supplier entry level - R12

Hi,

We are planning to implement 12.1.3.

I have seen lots of notes on defaulting the Payment Method for a supplier (to mimic R11), however, can't find anything on making it mandatory at the supplier level. Has anyone done this?

I understand there are defaulting rules that can be setup for an invoice, however, we want to setup the payment method at the supplier (R12 seems to look at site and then supplier) so that we can avoid issues at the invoicing level...(just overrides at the invoice for certain circumstances).  

The invoice entry seems to check for a payment method and does not let you save an invoice without one.  Am I missing something to make it mandatory at the supplier / site level?