Whatever he does, he can't just go cold turkey on the meds as this can have repercusions on his immediate health (and possibly his tcell and VL surrugate markers).
A fast, if anything, will create lower CD4 counts as these helper cells will leave the blood stream (where it's measured) to go do their job on various tissues and this is a good thing. If you test yout CD4s after a big meal they will likely be higher than if you had your test done in the morning before breakfast, when your immune system is repairing the body. I wonder what a fast would do to a viral load though, since these tests pick up genetic fragments that is believed to be HIV, instead of counting the amount of virus in the blood stream, as most people believe it does (google yourself what Kary Mullis, the inventor of the PCR technique behind the viral load exam, has to say about its use in AIDS treatment. He won a Nobel Prize for it in 94, and says HIV=AIDS is a bogus claim). Many, like him, believes AIDS is a toxic and malnutrition syndrome.
Before I did my first fast I talked to someone who had done it. Even though he didn't stop taking his meds, he got rid of some health problems, such as a fungus infection. HIV meds are extremelly toxic, so I think fasting is a great idea for those choosing to take medication as a way to counter balance its side effects.
I personally don't take meds, don't monitor CD4s, and couldn't care less about my viral load. My health is great and that is what I chose to monitor. But this is a topic for another message board...
I wish you and your partner the best in your search for health. Good luck!