Too much hassle.
Setup a proxy server instead, a good on that supports SOCKS5 and FTP as well as HTTP. Be sure to use bizzare port numbers like 32961 for HTTP, so that the average port scanner will not find it before it's kicked off. If the proxy server supports authentication, then use that.
Then, open up the office routing, punch a hole through the office firewall to enable the proxy server to be seen from the internet using port forwarding.