Actually, if I remember correctly, this was the reason why some people experienced a whole lot of problems signing into WLM not long ago.
What would happen was that smileys would not count as text in nicknames, yet when the connection was going to be made, every letter or symbol was counted. When the person tried connecting to the server, there was too many characters, making the server encounter difficulties and the person not being able to connect.
All that story to say that even if there was any way to do this, you wouldn't want to do it anyways.
/ 
