I think the excitement and anticipation of a concert gives that sparkling magic and spontaneity to performances. As a grand-student of Arrau, my professor used to tell me stories about Arrau performing outside in poor regions of S. America, and chickens would fly out of the piano as he played, and bench legs would break... remaining focused and relaxed amidst distractions was a critical part of my teaching.
If you really want to try to re-create the nerves of a concert in a controlled setting (in order to "practice" overcoming them), here are some methods my professors and colleagues use (I kid you not on some of these):
1. Get dressed up in your concert dress during those last few practices before the big performance. Women, wear your heels!
2. Recruit a friend to help out on this one: Start playing your piece. At some random point during your playing, have your friend pop a balloon behind your head. This does several things: you know that at some point, a balloon will pop, so there is a little anticipation before it happens; when the balloon pops, you may be startled and yanked out of that dreamy, focused state; after the balloon pops, your adrenaline will be kicking and you will be a little punchy at the keys. All of these responses are good to experience in practice --- the one time you're on stage performing and a door slams or a wheelchair tire pops (it's happened), you will chuckle and keep playing, unfazed, thanking that balloon for preparing you.
3. "Strip-Mozart." Get a bunch of your really close pianist friends together for a lovely evening 'round the piano. Everyone has to perform one piece. If you make a mistake but no one notices, keep going. BUT, if you make a mistake and it's noticed by someone, they have to call it within 5 seconds. At that point, you stop playing and remove one article of clothing. Then you begin again. The entire scenario is stressful, but very fun and very beneficial for practicing playing under stress. Your hands will shake, you're heart will be thumping, you will not be as focused as you'd like to be... Quite an experience.
Enjoy the nerves, though, and use them to your advantage! Don't fight them --- they're the sensation that distinguishes you from the audience!
