So you should be able to go your hosting panel, and create a 3rd level host.
A 3rd level host is the host before the first "dot".
TLD = Top Level Domain - .net / .com / .org
2nd LD = the domain name =microsoft.com
3rd level = the host www / ftp / myhost.x.y
etc.
So once you create the 3rd level host, you can just set it up to immediately fwd: to another domain (e.g. foldingstats.folding.org) or whatever.
I have this similar setup. Except I have several TLDs all with the same domain name.
e.g.
www.myhost.net, ftp.myhost.net, docs.myhost.net
These all resolve to the same IP, since they live behind the same Firewall. I just forward the correct "service" to the correct box.
primary IP = 99.99.99.100 for instance
When a packet hits the firewall:
www goes to web server 1.1.1.10
ftp goes to FTP server 1.1.1.20
Docs goes to file server 1.1.1.30
etc.
In your case, you want it to forward to your WWW, since thats where the DynDns is setup
So no matter what happens, as long as DynDns keeps doing it's thing, you should be able to fwd: any hostname to your primary Domain, and have it resolve the main page via the redirect.
why can't you just hit your www directly and create a custom page for your folding stats ?
I am having trouble understanding why you have to hit your site via IP. If you have dyndns working you can just use the hostname