How to create a joint with sensor programatically?

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I'm trying to create a joint from a plugin code that would look as follows:

<joint name="joint_a_b" type="revolute">
    <parent>link_a</parent>
    <child>link_b</child>
    ...
    <sensor name="force_torque_a_b" type="force_torque">
        <always_on>true</always_on>
        <update_rate>1000</update_rate>
        <plugin name="breakable_a_b" filename="libBreakableJointPlugin.so">
            <breaking_force_N>1</breaking_force_N>
        </plugin>
    </sensor>
</joint>"

I was able to create the joint using physicsEngine->CreateJoint() and setting it's properties directly on the Joint object. However, I can't figure out how to attach a sensor to it. A sensor that uses a plugin. I tried to create the whole thing by creating an SDF object with the above XML and passing it to Joint::Load() method. But because that XML is not a full world or model description it get's rejected.

I also tried to make some sense out of sensors::create_sensor but I got stuck on the same problem with XML.