Look into Pranayama or Prana Breathing Techniques and use them while meditating, focus on them, nothing else. And if you have an itch, by all means scratch it!
Nothing in meditation says you have to remain 100% still at all times. People meditate as they practice yoga or tai chi. I meditate everytime I create art (in pencil, paint, charcoal, clay, metal, you name it). In fact it makes me lose track of time quite a lot!
If you're not a stay still type of person, why don't you get yourself a yoga or tai chi dvd. Once you memorize the motions, you can perform it without the dvd and focus on meditating during the moves. Afterwards, sit or lay down and give yourself some quality meditation. I find that meditation after exercising and performing a "cool down" is the best. Your mind is clearer, your body isn't restless, and the extra oxygen and endorphins running through your system makes you feel great.