Advance Payment linked with Purchase Order

Hi,

we need to configure Advance Payment in purchase order.the client requirement is,In payment terms we define advance rate and attach with supplier.then after entering the purchase order a batch job will be run and generate voucher instantly for Advance and then payment will be done.then receipt and voucher match process will start.but we have suggested that in PO take 2 line apart from the Stock.

1.Advance Payment with positive amount.

2.Advance Refund with negative amount.

so at the time of voucher match that will automatically set off with the invoice amount.

but the client is not ready with this solution.