I emailed King Arthur Flour ( they're great about answering baking questions) and got this reply:
"Thank you for your email. I do not recommend this. This would dramatically alter the composition, flavor,and performance of the starter."
Curious anyway, I'm gonna check this out for myself, with a measure of my existing starter and some tapioca flour, just to see what happens in 2-3 days.
I've heard about using rice flour for sourdough starter but have never tried it.
Here's a couple of articles that might interest you: