I would like to include something like (say) "Chapter 1" in my TOC, but not display it in the actual document text. I tried to use hidden text, but hidden text won't be included in the TOC, so that workaround didn't work.

Any suggestions?

You can manually insert a TC field that displays nothing in the document. If you also have a heading that appears, you would have two entries, though, in your TOC.

Otherwise, you can format text as white with a white background. However, that text is still there and still takes up room on the page.