Quick update. I decided to pull the trigger on a ski for him. I tried buying a used ski (thanks for the offers), but it's a pain in the butt buying used gear across the boarder (we are in Canada).
We went with a d3 ion2 - 64" from the local shop. The size should give him time to grow into it, and he seems to be progressing very fast on it. His first time out, he got a PB. After a couple weeks on it, he has ran the course a few times now at 32mph.
I will get him to try 22 off to switch it up as well, I like that idea.
At the end of the day, I am sure the tra would have been fine still, but I am convinced that the ski has allowed him to progress faster. Thanks for all the suggestions and comments.