This is some advice that I gave another CCer earlier today. When I get HU anymore I win a lot. You can use this or toss it, no problem.
This tends to be my biggest problem also. I'm too passive late in tourneys. But HU I can help you with.
When you are on the button, be aggresive. Always three or four bet on the button. Regardless of what you have or what position you are in chipwise. When the flop comes out, c-bet it with a 1/2 pot bet. Do this regardless of whether you hit the flop. Now, if you are called on your flop bet, reevaluate the situation. If you totally missed the flop, or don't have at least a strong draw, back off. If you lose it, you lose it, but don't put any more into it. If they bet back into you, fold.
This works great for me HU! And once I'm HU I win around 75% of the time. Yesterday I overcame an 8-1 chip disadvantage using this strategy. Especially if you've been tighter than dick's hatband up to this point it's going to throw even the loosest opponent for a loop. It's a tough strategy to defend against since both of you get two cards and rarely do you both get two "good" cards.
Now, I'm learning to loosen up a little when it gets closer to the end, but I've still got a ways to go. But if you are three tables away from FT and catch an A with a decent kicker, toss some chips at it. Make it at least a 4 bet if you are trying to steal and look for good position to do so. You don't want to be throwing chips too much when you are in early position. But if you have AJs in 1st position, try for it, and if you get called look at the flop. If you missed, and the cards come out to where you think he missed also, toss a 1/2 pot bet out there. If he missed, he will more than likely fold. But I would'nt toss at draw heavy flops or paired flops.
But anyway, you do need to be more aggresive. My advice on the HU, I feel, is gold. My advice on late tourney play though, I'm still working on. So take it or leave it on that one.
Edit: From time to time you will run into someone in HU that will catch on to your strategy of betting the button. When this happens they will tend to go all in whenever you bet. I usually let them do this twice (to make sure it wasn't a fluke when they caught high pockets). After that, you have to tighten back up. Play a couple of hands just completing the blind and let them get comfortable again. Then, when you do catch a bigger hand (77+, AJo+) 4 bet it again. Usually, they will fold. But sometimes you can get them to call and that is a great opportunity to slow play the flop if you hit big. If you do hit big (catch your ace or make a set) either check it to them or make a small 1x/2x bet to try and induce an all in from them.
After that, go back to tight for a couple of hands and work back into your strategy slowly.