well, I just try to remind them that the psychologist is not the one that hurt them. She is the one that wants to HELP them.
For me, mine only write, too. I tend to try to get in there and start with coloring, that mellows one out enough so that she can be just a tad distracted from all the ruckus with what's going on.
Then I usually have T ask a Question and write the answer with the non-dominant hand.
IDK what will work for you, but I hope that this helps some.

Good Luck,
BJ