If you're anatomically male?
Ummm, pull your pants down in front of him, that should be enough. You want a recommendation to have that changed, having this test does nothing to obtain that goal.
Find out EXACTLY he hopes to accomplish with it, and what the results will mean before you even consider doing this test. Know what you are going to get from this BEFORE you bother. You want a letter for surgery, not a letter you can show that says "I'm intersexxed". Don't accept "perhaps" know what will happen.
My understanding is that this isn't a cheap test to have done. How many hoops and how much money does one need to spend to get a recommendation.