When I was down at the National Institute of health for a study on my Propionic Academia I got diagnosed with something called Chorea which is a abnormal involuntary movement disorder. This can meditation at times very difficult for me. Mostly I have harder time keeping my left arm still more than my right. Fortunately I have out though practice a few thing's that has helped me cope with this during my meditation.
Don't get stressed out or frustrated - When I first started I would get a bit aggravate it at the fact that I was a hard time staying completely still while meditating, I found I remain calm I can find stillness a little bit quicker.
2. Slightly rocking - Sometimes if I'm having trouble finding stillness I will add a slight rock to my meditation this takes away from the frustration of trying to stay completely still and I'm still able to find that moment of zen.
3. Bring my full focus to the body party I am having trouble with. Sometimes I'll simply bring my full awareness to a specific body part that I'm having a hard time with then that becomes my meditation.
4. Yoga - Yoga can be great form of meditation if you have a really hard time staying still during meditation. Just be sure to do your best to focus on your movements and your breathing.
Those are some ways I personally deal with having Corea and still being to meditate!