This is going to sound really silly, but it worked for me. I wrote a very long letter to someone once, and really poured my heart out. It was something like 9 pages long. And then I went outside and burnt it. As the smoke went up and away, I imagined all my words, my emotions, and everything else connected to the relationship being carried along with it. And then it was all gone.
I did this once. I even suspended the pieces of a letter in the candle and burned it over a period of a couple of weeks. It felt really good to have a place to pour that nervous energy, and a tangible way to see it disperse.
Hm. Maybe I'll do that again instead of writing angry emails I never send.