APA Style Guide to Electronic References license question

["Betty Kellogg" <bkellogg@nu.edu>]

I had a question about this paragraph in the license for the .pdf 
ebook version of the APA Style Guide to Electronic References.

http://forms.apa.org/books/styleguide/electronic.pdf

Licensee is granted the right by the Licensor to print copies of 
APA Style Guide to Electronic References equal to, but not 
greater than, the number of print copies in all available formats 
(hardcover, softcover, and spiralbound) of the Publication Manual 
of the American Psychological Association(r), Fifth Edition, that 
the Licensee possesses in its holdings.

Rights to print additional copies above and beyond this number 
must be separately purchased, and are not granted under this 
license.

I can't think of a way to monitor the number of times a .pdf 
document is printed. I might be able to change the document 
security to disable printing, but the patron could save it to 
their computer and print the document from there.  Does anyone 
have any ideas that would allow me to enforce the license 
restriction?

Betty Kellogg
Research & Electronic Resource Coordinator
National University Library
San Diego, CA