Database-based alternatives to tsearch2?

I've seen questions asked on the list about alternatives to tsearch2, but
not for the type of full text indexing I'm looking for.

I'm looking for a non index-based full text indexing - one that stores the
information as table data instead of index data. I do not need to implement
SQL operators for searches. The application library would need to implement
the actual word search.

Indexes are too fragile. Our documents will be offline, and re-indexing
would be impossible. Additionally, as I undertstand it, tsearch2 doesn't
scale to the numbers I need (hundreds of millions of documents).

Is anyone aware of any such solutions for PostgreSQL, open source or
otherwise?

Thanks

Wes