I think what he means is that criminals shouldn’t be given better conditions than the average person, not anyone anywhere.
Well, then there’s nothing to worry about, since prison is not, and is not likely to become, a desirable alternative to the quality of life of the average American. 
David answered the original question well, but I thought I’d take a stab at it too. The confusion stems from a misunderstanding of the phrase “a murderer forfeits his own right to life.” This phrase means that you may morally use lethal force if necessary to protect yourself or others from a murderer. It does not mean that you may shoot the criminal in the back as he is fleeing, nor that you may later hunt him down and cut his throat in his sleep (to protect the innocent, guilt and punishment must be determined objectively so the courts will, rightly, try you for murder if you do this). It certainly does not mean that the criminal becomes your property, a rightless serf that you may use for whatever purpose you wish.
In the case of capital punishment or life imprisonment there is no rehabilitation, so the purpose of the punishment is to deter others from comitting the same crime, and to prevent anyone else from becoming a victim of the criminal. A just deterrent must fit the crime, and torture (which using someone for medical experimentation certainly is) does not fit any crime. Although there is nothing morally wrong with permitting someone sentenced to death to volunteer for experimentation, offering to commute his sentence to life imprisonment if he accepts can in no way be considered a free choice. Consent under threat of death is not valid, and just because a criminal might agree to be a medical experiment, be a bulletproof vest test dummy, play a round of Russian roulette on national TV, or any other macabre deal in exchange for life imprisonment should he survive, that does not mean that those programs are right. The death penalty or imprisonment are objective punishments that are defined and knowable. They are objective. Sentencing someone to “whatever effects this experimental drug may have on you” is not, and is not at all just.
Finally this idea of extracting benefits from the criminal and conferring them unearned upon the general populace so “some good can come of them” is pure collectivism; it implies that men are interchangeable cogs with no individual moral import. The criminal did not harm “society”; he committed an injustice upon a unique, irreplaceable individual, and using him to test a cure for AIDS, or baldness, or heck just carving him up for transplant material (which would be a much more efficient way of using him to directly save lives) does not make up for it. Conferring these benefits on uninvolved third parties, as if one man’s gain can balance another’s loss, does not restore some great cosmic order. It merely piles one crime atop another.
Not to mention the political danger of making voters or government officials expect benefits from each conviction…