what you are asking for is a mechanism to tentatively add a transaction and then dispute it later.
I don't think that's what he means. The transaction will be made completely, but both will hold part of the key required to spend that money. If they are satisfied they ship the money to the appropriate person. There is not disputing with the block chain. They either work it out and use the code like everyone else does for all transactions, or they don't work it out and the money stays locked up.