If the gate on Parnassia is open, get in and locate one of the supervisors walking around. They will allow you to take a few pictures, I did this last friday.
Makes you wonder why an event with such a large regional impact (last time there were 11,000 visitors) has almost no information on the Internet or Facebook.
Well I was there today, and I have seen the fences all around the outside area of the museum. There is a tent for ticket control and access to the area.
Sneaking in is always possible but not advisable i guess.