The most likely method that Al-Qaeda would use in an American prison (on inmates who are not Arabs) is an appeal to the inmates’ sense of being treated poorly by American society. 

The people who are in prisons are very likely to feel as if American society has treated them badly.  Many of them are likely to feel as if they have not been given a fair chance in life.  This may be particularly true if they are members of minority groups (these are the people Al-Qaeda has tended to try to recruit) because minorities have been treated poorly in the past and are, arguably, still treated poorly in some ways. Because these inmates feel that they have been poorly treated, they may be more likely to respond to someone who sympathizes with them and agrees that they have been poorly treated.  If that recruiter then treats them well and offers them a chance to get back at American society, they might be persuaded.

Thus, the most likely method to be used in recruiting American (non-Arab) prison inmates is to play on their feeling of being treated poorly by American society, to give them a sense of being treated well by Al-Qaeda, and to offer them a way to get revenge.