I have a model that has an arm with a short sleeve on it. At the moment, the clothing and body are all part of the same mesh (the attached images are using a simplified version of my setup).

I'm trying to rig my character using rigify. After generating the rig, I parent my mesh to the new rig by pressing Ctrl-P and select Armature Deform with Automatic Weights. While this does bind the arm part of my model correctly, it does not seem to affect the sleeve.

How do I bind my sleve?