If your lab is behind a NAT from the real internet, you will want just one "master" node connecting to the internet (with port-forwarding of the bitcoin port to that machine if you have sysadmin access to do so). then all other internal Bitcoins should connect to it by specifying just the master's IP address with the "connect" command-line option.
Interesting but I'm not a "super techie" to set this in place I think. I would be great though if I could and let the participants mine some coins (they would love it).
Any tutorials to set up an own testnet?
Thanks!