WheelJoint2D: using motor and allowing free spin

I am trying to make a simple 2d game consisting of controlling a 2d motorbike on platforms. I have WheelJoint2Ds set up for the wheels, and I want to use the motor function of the WheelJoint2D to power the back wheel and make the bike move.

The problem is that I want to be able to power the wheel but them 'release' the motor so that it no longer controls wheel speed. At a motor speed of 0, the motor effectively acts as a brake, not allowing the wheel to move. This means it won't roll down hills or coast realistically.

I was wondering if there is a way to 'release' the motor so that the wheel will act similarly to a WheelJoint2D without 'use motor' checked while still being able to apply power to the wheel.