I assume there must be free web-ssh servers. Mindterm does this, but I don't know if it is free.
If your box is not running a webserver or ftp server just have your ssh server listen on one of those ports. That's the easiest way to circumvent the firewall.
If not you could just try some weird ports--the firewall may not block *everything*.
Webmin gives you control of your machine but that's an entirely different animal from what you're talking about.