>There is no practice that simulates anxiety.

Ah, but there is. Once you go through few interviews you get less anxious about the next one. Which means, that if this is a serious problem for you, and you expect some important interview in the future, then you have to go and interview with some other companies before to gain practice, and may be even get some job offer you'll like more than the one you are hoping for.

The whole point of the parent argument is that there are conscious steps you can take to make whiteboard writing not stressful for you. Just practice for ten hours solving problems on it and it will be as natural as writing on paper.