how do I hold the wheel and the bar at the same time?
Place the wheel in the corner betwixt floor and wall. Push the end of the wrench towards the corner. The harder you push on the wrench, the greater the reaction at the contact points and therefore the friction reacting against the wrench torque.
Yeah, I thought that clamping it would be no good, it would just torque off.
If I go for a breaker bar, how do I hold the wheel and the bar at the same time?