Services filtered by a proxy

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http://serverfault.com – I am in a network with clients, a proxy, and a router/gateway. The proxy is set by default in every client, and only allows the TCP ports 80 and 443 and the UDP port 53. I need to be able to reach another services (like SSH) through the gateway. I've tried a VPN(openVPN running on port 443) but the connection failed(i don't really know the reason). What can be done? May i somehow connect directly to the gateway(as it is in the same network)? (HowTos)