Validation of Vendor and Advance Payment Amount in F-47 and F-48

Business processes the down payment request using ME2DP, which allows DPR only on the PO vendor.

The business requirement is they will create a PO on vendor “X” and pay delivery charges to separate vendor “Y”, which is maintained in the PO pricing conditions (Delivery Cost).

Advance payment through ME2DP functionality is only possible for PO vendor only, hence for Delivery vendor they have to do advance payment through F-47 with reference to PO.

In this case standard system will allow advance payment request to any vendor other than X or Y also.

I have searched for any available Enhancement / Exit, however none of them is working in our system ECC 6.0 - EHP 6.

Request you to advise the best possible solution.