So the new idea is simple : I let user decides when he wants to cancel transaction and on which address he wants to get a refund.

And how do we do that?What are the commands for cancel transaction and refund address.
Good idea anyway and i hope its not a scam.

Nah its not a scam it works. in the bottom of the msg it sais "to cancel send a msg named "Cancel 4 to (your address)" to cancel.