I am glad someone actually tried it. With a K&N type filter you probably wont notice much difference. The main problem with the bonnevilles airbox isnt the filter its the entire setup. Most the gain is by using a pipe connected to a cone filter. The filter itself doesnt matter as much as everyone would have you believe.
If you have the money it will probably be worth it because you can clean and reoil it and they last much longer. You could probably have more success with an elbow at a 60% angle connected directly to the TB via a rubber coupler.