V8i VBA - I Want My Very Own PropertyHandler!

This has bugged me for a while.  I'd really really like to create my own category of properties to associate with elements.  Way easier for users to query than tags, and something that Navigator can display in clash results.  I've been able to successfully read these properties that other applications (i.e. InRoads) are able to create on their own (lucky ducks), but no success adding my own.  I'd like to mimic the custom approach shown below to adding metadata.  Any guidance would be greatly appreciated!!!

-Christopher Johnson