Payment Request between AR and AP which are in two different instances (R12 Refund Process)

Hello Guru's,

     We have a requirement on processing customer refunds from AR to AP. Our client is using AR, OM in a different oracle instance and AP, PO is in a different oracle instance (R12.1.3). Client wants to use the standard AR refund process where we can refund the customer through Payment Request Invoice in AP.

     Currently I am exploring if any option available to create payment request invoices manually with the same refund amount processed in AR as the refund attributes captured in AR will not be flown to AP.

    I understand we must need to create a custom interface and that interface should work in bi-directional to process payment requests and should also have the ability of handling payment request cancellations in AP.