I imagine the firewall is there for a reason, however I would think that tunneling ssh over an open port such as 80 or 21 (if ftp is allowed) might work. You could always forward port 80 on your router to your ssh server at home on whatever port it runs. I have not used it myself, but have you looked at:
corkscrew - tunnel TCP connections through HTTP proxies
If all else fails, there are also services like:
There are some security implications with this.