I'd take a creative approach and bind the server's IP to a separate folder with a text-document, like "README". People will be curious and open it... then I'd just tell them to stop using the server's IP and instead use the server's name. They'll be forced to change it to see the new files anyways, so you should be able to get everyone to switch.
And then just have the regular FTP server binded to the name. Should be possible, 'ey? As for a programmable way of figuring it out, that's a really good question.
EDIT: not too sure on how it works on Windows, but if you have an FTP running on the IP and the name of the server, you should be able to view the logs too and see which server is being accessed by what IP. Although this is coming from a Linux guy. :p