I have a dim memory seeing a clip where a guy showed an ankle lock variation, where instead of going under with the same side arm, you passed the opposite side arm under and figure foured, to put more torque on it.
Something else in the 'I can't believe its not heel hooks!' vein; I think the strongest methods of performing leg locks all follow a sort of 'corkscrew' principle, and to increase your finishes you look for ways to incorporate that.
Like with the toe hold, you snake the looping arm in deeper and grab around foot like a wrist ride from the back, and grab around the big toes with the other arm. The let's you keep the leg tight while 'corkscrewing' the foot down and in around (ie, the old 'toes to the butt' addage), much like a well done heel hook.