Well, you suggested to use multiple TOCs, I want an index.
The use case is this: I have a library of song lyrics. I want to compound those in ebook of some sort. There are a lot of songs from different artists and albums. I created a simple structure in HTML where every h1 is the artist, h2 is the album and h3 is the song title. Then the song lyrics are in a PRE tag after. This is ordered by Artist/Album so it works out okay in the main TOC: I take only H1 tags and get a table of contents for authors. So far so good.
But making a (sorted!) TOC for song titles doesn't make sense anymore, because the content is sorted by Artist. Hence the idea of using indexes instead. The idea would be to have an index of all song titles at the end of the ePUB, ordered by song name.