[NTG-context] Unusual TOC

Hi, I'm typesetting a book where prose and verse alternate in chapters, i.e., you have one chapter of prose, one of verse, one of prose etc. I would like to generate a TOC for that book, but chapters have no name or numbers. I was told by the author that the usual thing to do is to take the first few words of each chapter and use those in the index. I know how to do that using a few small tricks, but I would like to know if there's a standard way to do that. Are you aware of any? Thanks, Maurício