Receivables Refund Processing with Centralized AP

Has anyone customized receivables refund processing to support refunds when there is NOT a one-to-one-to-one relationship between the AR, AP and GL Business Units (BU)? 

We have centralized AP processing so the AP BU points to one centralized, administrative GL BU.  We have (sort of) centralized our AR processing by setting up AR BUs used only by our administrative, service center personnel.  In the end, we have 40+ AR BUs, each pointing to its own independent, operating GL BU, which is not the same as the centralized GL BU used for AP processing.