Since stopovers are only allowed for awards between two Regions, the only way you could get away with this would be to book LAX/SFO-ORD as your outbound with ORD-IAH-LAX/SFO on the return (if they'll allow this routing) and just get off the plane at IAH. Checked baggage would be your greatest enemy unless they let you book a clever overnight connection where you could claim your bags at IAH.