I downloaded wireshark and started searching for packets when you login to MSN Messenger.
It looks like there is a "policy" packet that is fired to MSN when you first login and it has contained in it what I believe the source of the issue is.
Unless you go to the trouble of intercepting this packet and changing what it says before it hits the software, I'm not sure there is much we can do. There might be a way to hex edit MSN itself to always make this "enabled" - but again, might not be worth the effort.
BINGO.