Are there workarounds to sending URLs MS doesn't allow through Windows Live Messenger?

I'm currently omitting the http:// part so it's sent as plain text, but I'd prefer something clickable. All subdomains offered by no-ip.org's free service seem to be blocked

tbh, they are usually blocked for a reason, and its usually to protect the innocent and naive. Start looking for ways around it, and the spammers and viruses will start getting around them too.