Well, there goes "3rd way" for now. I was [initially]disappointed to finally find this in the documentation:
Individual pages in a Pollen project don’t know anything about how they’re connected to other pages. In theory, you could maintain this information within the source files.
Pollen's idea for organizing multiple pages of content is to dictate that each page is its own isolated kingdom, and to use a static list of pages stored as a separate file, to organize them.
Apparently, Pollen contemplates no way for files to provide information about themselves for use in other files, no way for blocks of content to discover and relate to each other except through their relative positions in a rigid hierarchy (or a flat list).
(update: It turns out that the excerpt from the docs above isn't strictly true, and there are mechanisms for Pollen pages to parse data out of other pages; see below.)