<p>I agree with the suggestion of using something to follow the words. I did a speed reading course about a hundred years ago and one of the things I learned is that as we read a passage we read ahead and also backtrack without realizing it. In the class they had a gadget that covered everything but the line you were reading to stop you from doing that. After a while this trained you to not do it. I went to the class thinking it was stupid (it was a class my company would send us on ) because i was already a pretty fast reader. I really sped up by the end of the week. </p>
<p>Although this is a different situation the same technique might help as it focuses you more which might take away the need for the subvocalization. You could try holding a piece of paper under or over the line to make you focus on the line. Not sure if you can do that in the exam though. Following the line with your finger would have the same effect.</p>