My hosting service provider Interneto vizija (who also owns serveriai.lt and dedikuoti.lt) just recently enabled me to directly edit DNS records of my domain seimys.com. It was a trial and error at first, but finally all is set up. The goal was to set up one of my sub-domains (my.seimys.com) to direct users to my 2TB FTP server (NAS Box). My home IP (TEO Zebra ISP) hasn't change for as long as I can remember.
The trick is to add another A line into my DNS record:
my A <HOME IP>
And that's it! Now I can happily SSH home, if I leave my PC turned on.
By the way, don't forget to add the other necessary lines (www, ftp). If you don't - your www.something.com won't work.