How about making a script?
Very Easy to do...
EDIT:
In a VERY easy way:
code:
function OnEvent_Initialize(bMessengerStart)
{
MsgPlus.LockMessenger(true);
}
That will lock msn as soon as it starts
EDIT2: Thinking about it, it's kinda useless, cause Plus! won't go out of Locked mode if msn disconnects...