Apply AR Payment by Party and not Customer Account

For our client, we have setup a single party with multiple customer accounts for their corporate accounts.

Taking the example below, think of it that each store here is setup as a customer account, with its own bill/ship-to. However each of these 3 customer accounts have been created under a single party. Now invoices are sent to the party or Bigmart Conglomerate /HQ via EDI every day. They typically send one single payment or check for all of their invoices across all of these 3 stores to us.

• How do we apply this single check or payment to all of the invoices for all the 3 store customer accounts?