Good idea, but then the main question is - why the heck BOTHER WITH ENCRYPTING THIS ONE?
Contrary. SEND HIM THE SOURCE.
Allow him to use those to build a testbed, modify them with debug and test code for HIS code.
What you basically do is called mocking, and is a good part of testing. Fake environments are standard practice, and they are a LOT more useful when they can be extended as a test requires.