You can serve up two sites but they'll have to be running in the same server program. In each Handler, you can get the full request URI which will tell you whether your user was navigating to ctd.noip.me or tomduncan.noip.me and then you can decide what content to serve to the user. In this case, you shouldn't give users direct access to statically served pages as they might have ambiguous links.
Another option is to have one server be secure (default port 443) and the other be insecure (default port 80) and then you can have two separate, normal server applications serving up static pages.
You can also specify port numbers in your domain name: ctd.noip.me:1111 and tomduncan.noip.me:2222 and then you could have these go to two separate server programs running on the same computer.