Joscelyn Godwin also recently wrote an article "Esotericism without Religion: Philip Pullman's His Dark Materials" which features in the collection 'Esotericism, Art & Imagination (Michigan State University Press, 0-87013-819-7
This might be where Godwin came to Pullmann's attention, or they might be friends, which is indeed the origin of the joke.
Otherwise, Godwin also has a new, full length book on Kircher that should be appearing soon, if it hasn't already.
I haven't time to look at all the books in that list, but I am sure they will be analysed in detail in a PhD in the future:
Pullman's full name is Philip Nicholas Outram Pullman
Beaumont Street is where the publisher is based.
Marisa Coulter is a character in The Dark Materials
The name Karel Powers has been used to write some fanfiction on the 'net.
Giovanni Battista Kremer: conflation of Piranesi's forenames & Cremer the alchemist??