Punishments for 6 year old?

My step son is 6, going on 7. His mom and stepdad have told me things they do that work at home to punish him (we have him during the week right now whereas usually he's just with us on the weekends.) I take care of him and his older sister while their dad is at work during the day and even though I've been caring for him since before he was 2, it's like he's suddenly forgotten how to listen to me. I've tried EVERYTHING with him. From sending him to his room (it's enjoyable or a good time to nap for him so he doesn't care.) to raising my voice (which redirects him for a while but then I have to do it again when he starts acting up again and it just hurts my throat.) I've tried time-outs with nose in the corner to sitting on the couch and not being able to play to even letting his sister take care of it when he hurts her. Nothing is working and I'm out of ideas. As a step-mom I don't feel comfortable spanking and while I may do it when my own child is old enough and misbehaving like he is, I honestly don't think it would even work with my stepson. Recently I've been making him run laps around our backyard (not that big) but it seems like he dreads doing it but doesn't really care that he has to when he does get in trouble. I guess what I'm looking for is creative (non corporal) punishments that will work for a child who seems not to care when he does get in trouble. Any ideas?