Billing multiple remit to addresses for one bank

How do people setup multiple remit to addresses for different lockboxes  when the setup for the External Bank associated with a single bank account only allows only one Bank Branch?

We share the one bank account with AP and Expenses as well as having about 3 lockboxes of our own.  The Remit to information from both Online Billing and setup pages for Bill Source and Type pulls

data only link to bank code, bank account key and the specific valid bank account number .  Attached is picture of External Bank Account associated with one and only one GL BU and one Bank Branch.