Yes. Here's some info on his setup. It tracked the motion of his cheek, which he could still control, to stop on a letter. It scanned through the alphabet and he had to pull it up at the right time.
“I can also give lectures. I write the lecture beforehand then save it to disk. I can then use a part of the ACAT software called Lecture Manager to send it to the speech synthesiser a paragraph at a time. It works quite well and I can try out the lecture and polish it before I give it.”
http://www.hawking.org.uk/the-computer.html
I also just started typing that in present tense ('tracks'...) and had to pull myself up. :(