While I toy with the idea of taking seriously the old Byzantine attitude that mutilation (usually blinding, though in the present case, removal of some other body parts in addition might have been warranted) should be substituted for execution, as it gives the miscreant a greater chance to repent of his sins, I am mystified why drastic overdoses of opiates are not used for executions. Surely we should be able to estimate the LD100 for morphine for any given body weight, accounting for any tolerance built up in the case of opiate addicts, double the amount, and administer this as the means of execution to give a genuinely painless, even blissful, death to those found guilty of crimes warranting execution.
Why the hell would you want to do that?