Trading with WalMart same AS2 amp EDI IDbs different certificates

We are having a problem where we have several internal trading partners that trade with WalMart. Each trading partner must have their own connectivity with WalMart. The problem is that WalMart uses the same AS2 name, same EDI IDs but a different certificate for each trading partner.

The problem is that when we send an EDIINT document to TN, TN will pick the first match found for the AS2_TO ID. The MDN will then fail because the AS2 transmission was sent with the wrong certificate.

Does anyone have any ideas on how to get around this problem? (We are on IS 6.1.)