Do NOT nit it up: at 400bb you should be in there trying to get the most from your massive implied odds
If you only play big hands deep stacked people are only going to give you action when the crack your overpair, as you will have basically announced what your hand is by your tight play.
Some random advice (all of which I'm sure you already know):
1. Try not to play out of position with one pair hands like AQo. If you do, play a bit more passively, and keep the pot small.
2. Play ALOT of hands in position, especially against the weaker players at the table, or those that you think you have a line/read on their play.
3. Don't be afraid to try to make some plays: squeeze, float, 4bet steal, etc. If they don't work out, well, you should be deep enough that your 'M' wont be effected too badly early on.
4. Force yourself to think WAY MORE about your opponents hand/range than your own in this tournament, more than you ever have before-- you will be surprised how often you find spots where your own cards don't matter in the least. The more you can do this, the longer throughout the tournament you can maintain the discipline to do it as fatigue sets in, the better you will do.
4. Identify your target: value bet the calling stations, bluff the weak-tight nits on that third flush card. NOT
the other way around!
5. Make sure you have some sort of "endurance plan" whereby you are not going to get tired and hungry throughout the long event. Have food, drink, chamber pot, and masseuse nearby.
6. Run good.