I searched around the web, even in the official SCII com forums, but I could not get an exact answer on this question:
"Is LAN with SCII definitely not possible or is there a way to get the PCs inside the LAN connected even through the Battle.NET without connecting the computers via Internet?"
I heard about work-arounds, where you still use battle net but after connecting to the certain players you let the connection run over the local network.