You can tunnel vnc over ssh by following the steps given in the above URL which boils down to this.
1. Start vncserver on extranet tier by typing: vncserver :5
2. On the jumpbox server type:
ssh -v -l 5905:extranet_hostname:5905 extranet_hostname
4. Create a file test.htm in $COMMON_TOP/portal/$CONTEXT_NAME directory with the text "You have reached extranet server