For one thing, "An Introduction to Programming with Mathematica" is on his Clojure bookshelf: http://www.amazon.com/Clojure-Bookshelf/lm/R3LG3ZBZS4GCTH
A quick Googling will show you that Rich has popped his head into a bunch of conversations where both Clojure and Mathematica are mentioned. He's also mentioned it in a talk or two.