How to add a bone to mannequin skeleton with blender and UeToRigify addon ?

Hello,

I just want to add a bone to the mannequin, child of the root bone, i’m using blender and the new add-on UeToRigify.

For now i add my bone in “meta rig” mode but my problem is to transfer it to the source skeleton and to export it.

Anyone can help me ?