I'm not sure how you could offer some thing without giving them a numerical input of what the offer is worth
I might be able to add a PM in (atm you don't get notifications of any bids for any listing types unless you are outbid). This listingtype calculates the winner at the end and notifies the winner, the losers, and the 'seller' - that is the person who is wanting the item.
A future listingtype will give more control over selective offer acceptance.