Why use four characters when you can use three?
On a related note, here's how to abuse the concept of URL shorteners in order to produce messages in which embedding a URL costs zero additional characters:
http://www.byrnehobart.com/blog/steganographic-typo-based-ur...
Maybe use a magic pattern in the first few characters to indicate a url ID is present.
"It was so clearly a choice of doing good work xor being an insider that I was forced to see the distinction."