DNS2GO, the dynamic DNS provider, has an option to redirect anything beginning with "www." to any port. It is specifically to allow bypassing providers that attempt to thwart home web servers by blocking port 80. Other dynamic DNS providers may offer a similar feature.
You would need to reconfigure e-smith to run on something other than port 80, for example port 8080. I think this has been discussed on the forums before, so I'll leave you to search for that particular bit.
Once done,
www.yourdomain.dns2go.com would be redirected to yourdomain:8080 thereby running the blockade on port 80. Other URIs not starting with "www." are not affected, so FTP and SSH for example work normally.
hth
Scott