As non-chalantly as possible, pull out a stopwatch and say, "You have to do these wallsits."
Kid: "I don't want to do them, I'm not going to."
Parent: gazing at stopwatch "You got 10 seconds to hop on over there against the wall bud. Otherwise it's white rice for dinner for a week."
Parent: "Grumbling and pouting is a bad habit, as well as laziness. Gotta get it out of you."
Our approach with kids was - "You clean your room or I will. I'll put everything in a hefty bag and take it to the basement for two weeks."
A couple trips to the basement with a bag of toys, favorite shoes, etc. and the problem was solved.
I'm sure there's some doormat parent reading this saying to themselves oh dear goodness now that's just awful. They'll suffer emotional abuse over that!