Go to Mosehansen's site, here:
https://www.mosehansen.dk/cgi-bin/dom2.pl
Then find the game in Open games, and snatch the port number. You will then need to launch Dominions and to go in the network screen;
www.mosehansen.dk should for for an IP, and the port number will be displayed on the game page.
Create a Pretender for an unclaimed nation as usual, connect to the server, and upload your Pretender. Do *not* hit "Start the game", and disconnect instead. Then you should register on Mosehansen, and confess that you are playing one of the anonymous nations.