i don't know if anything like this is possible, but how about signing him and sticking a behavioural clause in his contract i.e. if he is summoned to court for any offence during his time at the club we have the option to immediately cancel his contract.
It would ensure that he keeps on the straight and narrow as well as possibly pleasing some of the fans that are unsure about him because of his past. I think it would work for him as he could really prove to people that he has rehabilitated himself even by agreeing to such a clause.