Very secure firewall and need to RDP into a pc behind it

I have a WinXP pc behind a cisco firewall (we have no access to this firewall since a third party owns it) and all ports are blocked (incoming and outgoing) except for 80 and 443. From the pc, we can only surf the web, absolutely nothing else.

How can I remote INTO this winxp pc from the outside over the internet?
I tried rdp but the ports are blocked and have no access to add a port trigger.
I also tried RAdmin and set it to port 80, but no luck.
Would a agent based remote desktop utility work? Any suggestions?

Thanks.