How to store per-track user data?

Hi Reaper gurus,

I'm not able to find any APIs that allow one to associate user data to a track. If I've missed something, please administer a proper cluebatting.

Meanwhile, there are of course options to store either global state or project-level state, and one could store project state using the track UUID as the key.

There are two problems with this approach though:
1. User data is not carried over when the track is duplicated
2. The script must periodically sweep the stored data to make sure that data is properly cleaned up for deleted tracks.

#2 is a minor inconvenience, but #1 is something I don't have a solution for.

Are there any APIs to deal with this use-case, or maybe some common patterns that others use to solve the problem?

Thanks!