I think that people who have diaetes and other chronically medicated diagnoses have done the Master-Cleanse probably some while doing meds and others while stopping. I know I've read many posts to that effect. I don't see how hiv meds would be any different.
Also, some are skeptical about a virus being a cause of aids (Clark and Andreas for instance). If that is the case the meds might not be the best treatment for your partner anyway. Sometimes, if it's not broke don't fix it.