Adding temporary documents to an existing index

[GeeWee]

I'm trying to use Tantivy, but I might have a bit of a special use-case. I have one large search index with data that is essentially static, and shared across all users.

However, some users also have some private documents in the same structure that needs to be searchable along with the existing large index. The private data is sensitive, volatile and I would prefer to not write it to disk, where the existing tantivy index resides.

Is there any way to write temporarily to a tantivy index without committing/persisting, or compose a search across multiple indexes?

I have not been able to find an API that allows me to do this. I could of course create a new temporary index with just the user-data in a RamDirectory, but that would mean that I would be unable to compare the scores across indexes, as they seem very different with my smaller index versus a bigger one.