Reversal of MIRO for half the amount

Hi Gurus,

I have an issue here wherein the situation is as follows-

1. GR has been done and later cancelled as goods have been returned to vendor
2. MIRO has been done, but now the business needs to reverse this. However the twist here is that the reversal needs to be done only for half the value as the contract terms state that in the event of return of goods, the vendor and business would bear half the costs

The resolution we're trying to figure out is how to reverse the MIRO for only half the amount so that we can achieve the following-

1. No difference to appear for the GR/IR account neither in terms of value nor quantity
2. Have payable reflecting for the vendor for half of the invoice value with document posting in a way that we can have this document reflecting in the PO history

Any suggestions/advice would be appreciated

Thank you,

Gaurav