vendor buys back invetory at cost, how do i set a SOE to do this?

We have a process where the vendor essentially buys back some of the inventory that they have sold to us.

It might be used for promotions, Recalls etc.

I need a way to key an order and cost that will flow through the standard warehouse process ( pick pack invoice) the sold to would be the vendor

and then post to the vendors account with a reason code.

Today our solution is to do an adjustment and then manually do a deduction from the vendors account in accounting.

Thank you