1v1 Death-Row fights. Why the hell not, I'm part barbarian at heart and we've already consigned these folk to death anyway, why the hell not let them fight it out on a field of glory (and blood). Humanitarian? Fuck that noise, let it be voluntary either you get the needle, the chair or the Colosseum. The winner gets a stay of execution but no parole and can choose to defend his title or retire to a solitary confinement.
This is assuming that in this Empire there are no appeals and lawyers have all been beheaded, shot, drawn and quartered, burned at the stake, etc.