Vendor return Process - Capture of delivery costs

My client has a scenario of vendor return with PO, where we indicate that the PO item is a return item. We use VL120B to create the DO and then do a PGI.

You can do the Vendor return with transaction MBRL as well. The accounting postings in this case will reverse the entire value including the delivery costs.

I do not have the same provision for PO returns. When we return the item through PO indicator, how to ensure that the item is return at WAC ?

Returning the item at Purchase Price without consideration of the deliver costs, will result in high WAC. How to resolve this issue. We cannot put negative in the condition type also, because system gives an error saying negative delivery cost is not allowed.

Could anyone advise on this?