Are you sure that it cannot be done? Conditions could be like "no Carthaginians on Sicily" (war=lost; lack of prestige and decent military), "money=low" (war exhaustion; and unwillingness to pay mercenaries); can searching for mercenaries in armies be done? and eventually delating them? (desertion)

Even if not, is it still possible to create some rebel stack under such conditions? We can assume rotation among Cart mercenaries, some still could go unpaid. Add a lot of Libians here (they had other reasons for fight) and you can have decent military uprising.

BTW, it should probably add some money to Carthage, as they went with mercenaries cheaper way (and at least this one time they realized what "patriotism" is)