For those with a time machine, or who might build one in the future, attached is a scan of the original invite for Ken & Roberta's house warming party on the 3rd September 1983, i.e. the one that Ken mentioned as having about 800 people attending. It should get you through the gate, and with the crowd size, it should be easy enough to blend in.
I've been thinking that a fan made game based on that plot and this event might be quite interesting. The photos available online provide enough detail to get the outside and inside layout, and guesses could be made as to how it might have looked in those days. The rooms and outside scenes would need to be populated with crowds of people, to cover the 800 who apparently attended. Not sure what the puzzles would look like though. Hmmm, maybe to secretly obtain a copy of the top secret King's Quest PC JR game, an early buggy version of which might be held in a safe within one of the rooms. At the time of this party, the KQ project was apparently well behind schedule (according to the Hackers book published in 1984), so it wouldn't be the complete game. The KQ developers were probably all at this party, even Arthur Abraham, as he didn't leave Sierra until a couple of months after that.
Edit: Or perhaps the goal would be to somehow obtain a keycard or whatever they used from a KQ dev whilst at the party, so that you can then sneak out to the secure KQ office location whilst everyone else is otherwise distracted by attendance at the party, gain entry, and once inside, fix some historical known KQ bug that existed in the original release.