Thanks! That sorted it for me...

For others reading this was the exact process:

- Highlight the whole TOC
- Ctrl + Shift + F9
- Now the table is in an editable mode, you can add whatever lines you like. I wasn't sure how to change what is linked to here but...
- Ctrl + Shift + F9 again and now the lines look like standard hyperlinks. You can change what they link to, including bookmarks, with right-click "Hyperlink..."

- If you do Update Table though, you'll lose your custom entries...