Search for World Premier of Kinect. There are two 'episodes'. The second is the E3 2010 Press Briefing which lasts 1 hour and 31 minutes.
You have to watch this in real time unfortunately, so you can't fast forward like other apps.
Also, DO NOT let it play to the end. If you get to the end and it backs out to the menu on it's own IT WILL NOT COUNT. Instead stop a minute or two short and you'll be fine.
Personally I had the achievement app snapped so I knew that it counted.
Then just repeat. Alot.