Guild Wars 2

I have tried Ultrasurf, battleping, and pingzapper. Would the only way to do it be to set up a proxy server on a computer that is not behind the Fortinet firewall?

Your screwed basically.
Any firewall that is blocking Proxies/Dynamic Port Allocation, is going to be hard to bypass.

Unless you have a remote ISP somewhere (LIKE YOUR PARENTS HOUSE) and you setup a PPTP VPN Connection back to that ISP and tunnel though it for all internet traffic (thats providing the firewall isnt blocking the GRE47+PPTP Communication ports to do it).

Alternatively you could pay for kitten .L.(stupid Anet Filter – Kitten on SSL?! Really?!) VPN service (20/month).

But otherwise, 99% of the time proxies are blocked when you see things like netscreen/Fortinet/SRX/ASA’s involved.