I have a Raspberry Pi running Raspbian Wheezy connected in "Site A", where the network is managed by a third party company and where all ports are closed the the Internet (for security reasons). So, there is no way for me to do any port forwarding to VNC, nor SSH or anything else. That means I just can't access it in any way other than locally, on-site.

However, I need to connect to that device on the X Desktop session (graphical interface) to do some maintenance, and I am located in let's say "Site B", which is nearly 300 miles away from site A.

I know you can do such tasks on Windows or x86 Linux computers with TeamViewer (we use it for our other hardware in the same location and it works like a charm), but since the Raspberry Pi is based on an ARM architecture, it isn't supported by TeamViewer yet.

If anyone has ever achieved this, I would be glad to hear how to do it!