Did you know SketchUp models - any SketchUp entity for that matter - can contain Attributes? In SketchUp parlance, an Attribute is a Name/Value pair. You may not have known about it because there is no UI to access them.
Just unzip the bundle in your Plugins directory and you're good to go.
This plug-in doesn't handle custom UIs for specific attributes or categories, but it could (should?) be extended to do so.
These details are provided for information only. No information here is legal advice and should not be used as such.