Well, the resounding responses to the positive made me look at alternative solutions...

Firstly, I have been in contact with nic.uni.cc, who have advised me that a Win32 client is in beta - they are unsure of a Linux client. Of course, a perl script could easily replicate it, or allow for it to be added to ddclient.
In the interim, the solution is quite simple. I chose to use dyndns.org for my example, as I use their MyCustomDNS (a fantastic service). It's worth noting that, while this solution can actually be applied to get around donating to use MyCustomDNS, that for USD$30, it's better to have the full range of options!
1) Firstly, set up a new "host" using dyndns.org's service. For the sake of example, I shall use foo.gotdns.com
2) Set up your e-smith box to support this domain. (This may involve changing the domain at the console to use the inbuilt dyndns clients, or you may even want to take the easier approach and get ddclient, which you can edit to do multiple domains etc. It also can get the IP address from Alcatel SpeedTouch Pro's and other routers/DSL modems! This has been covered enough times before, really...)
Don't forget to setup a virtual domain if necessary!
3) Next, set up your *free* uni.cc domain.
http://www.uni.cc (Free for personal *and* commercial use)
4) In the uni.cc "domain control panel," log in and choose the "configure" option. In the "Domain Name Service," choose Web Forwarding. Apply these changes and go back to the Control Panel.
5) You will now have an option to "Configure Web Forwarding." Pick this option.
Forward the domain to the "real address" of your dyndns host. Also, pick the "hide real address" option, so that you don't look like a prat!

In the case of the example, the forwarding address would be foo.gotdns.com
That's about it. You're done!
Any features that you want to set up, will be done as the foo.gotdns.com host, so you get your normal dyndns features. The uni.cc address will simply forward straight to it, invisibly.
Cheers,
Tom