Echoing *outgoing* messages to all presences

I have a user with the JID usr1@server/Desktop on my Openfire server, and that user has transports to MSN and GTalk via the Kraken gateway plugin. I’ve changed the route.all-resources property to “true” so that incoming messages from those transports are also sent to the user’s other presences, usr1@server/Laptop and usr1@server/Phone, which is the behaviour I want - however, I’m looking for a way to also echo outgoing messages to the user’s other presences (so by sending the message “hello” from the Desktop presence, the XMPP clients running with the Laptop and Phone presences appear to have sent the message “hello” too). This is primarily to help with logging conversations, and also so that the entire conversation with another person is visible at all presences. This probably isn’t possible without a protocol extension, but I’m interested in a definitive answer from someone who knows much more than I do.

I’m happy for this behaviour to affect all users, if that makes it any easier.