Two simple steps are needed to access macmini buildbot, which is connected to altair via VPN service.
ssh -N -f -L 10022:10.8.0.10:22 email@example.com
ssh -p 10022 videolan@localhost
where 10022 is the local port on your machine, 10.8.0.10 is the IP address of macmini, and 22 is the port macmini's sshd listens on.
ssh -N -f -L 15900:10.8.0.10:5900 firstname.lastname@example.org
Then, in your VNC/RDP client application, open localhost:15900.