Properly you need to create your own custom adapter (assuming
you use messaging) to store the last XX number of messages
Then when a user logs you setup a remote object to retrieve
the last number of messages from the server, and continue as
normal.
I am not sure if you can push a single message from a adapter
to a single client only, that's why I was thinking doing that last
XX number of items with a remote object.
Ries