Can a plugin inject data into the cascade after the page content is rendered, but before the whole page is rendered?

[pdaoust]

I'm trying to write an extension that parses the content of a page, generates some data, then passes the object into the data available to the page templates. Is that possible?

The use case is that I'm trying to generate a content outline as a nested structure, then pass that data on to the template which can render it as an on-page table of contents. I'm not looking for a ToC generating plugin; I've looked at those and they generate the markup for you, which I don't want -- not flexible enough. (But if I've missed a ToC plugin that just generates raw data for the template, I am interested in that!)