I have done CVSA tests on willing participants as an independent study and have seen trends that indicate that you can fool the test, IF...you believe what you are saying, or have brainwashed yourself into believing what you are saying.  If the tester goes by a written plan, then of course they will be able to be "gotten".  I think it boils down to a strategy, that the government probably does not want you to know about (hence the testers that follow a written test framework may be fooled by testees training themselves with another set framework)  If they "reaally" want to know, they'll most likely know. (note:  I am not a certified CVSA tester, nor do I currently work for the government (technically), I am only an enthusiast)

i think the site you are referring to is passacvsa.com.

"The CVSA examination requires completely different countermeasures compared to the polygraph. In order to obtain the desired result, passing the CVSA, you will need to practice the following response patterns.  The CVSA examiner is looking for one thing and one thing only. How you vocally respond to certain questions. As you well know, every time you speak to someone you are relaying information. What you may or may not know is that the way that you say particular words can relay that information in a positive
or negative fashion. 

Lets use the following example. Lets say that someone asked you this question.

“Do you believe that Susan is telling the truth?”

Your response is “Yeah, I believe her”.  The way that you say “Yeah, I believe her” can either be interpreted that [yes, you really do believe what she is saying is true] or [ yeah right, I believe her and by the way I’m the Queen of England]. Where you put the emphasis is what will determine a person's response. It is extremely important in the CVSA examination that how you say something is more important than what you say. This is the key to the CVSA examination.

In order for you to achieve a positive result on the CVSA examination you will need to respond to the
examiners questions in the following manner.

RELEVANT QUESTIONS
When the examiner asks you a relevant question you must always respond “YES” or “NO” in the same
exact way (with the same pitch, tone and breath output). The best way to do this is to answer the question right after you have finished inhaling.

For example:

CVSA examiner----”have you ever used drugs while you were at work? ”

Your response----You inhale normally, prior to starting to exhale you answer “NO” and then exhale the
remaining air that is in your lungs.

YOU MUST DO THIS EVERY TIME AND FOR EVERY RELEVANT QUESTION!!!!

CONTROL QUESTIONS
When the examiner asks you a control question you must always respond “YES” or “NO” in a variety of
ways. You must make sure that you vary your response for each and every control question.

For example:
CVSA examiner----“Can you drive a car?”

THE THREE VOCAL COUNTERMEASURES
Your 1st possible response----You inhale about 50% more than normal, answer “YES” and then exhale
the remaining air that is in your lungs. Doing this will make your response louder and higher in pitch.

Your 2nd possible response----You inhale normally and exhale normally making sure that you answer
“YES” at the end of your exhale. Doing this will vary the tone and pitch every time you answer this way.

Your 3rd possible response----You inhale normally and then swallow. Immediately after you swallow
you respond “YES” to the question. You then exhale as normal. Doing this countermeasure gives the
impression that you are bothered by the question as well as changing the pitch and tone of your response."

-WWW.PassaCVSA.com  Authored by:Steve Mickelson, Peter Andrews and Kyle Hunter