I'm not sure if anyone is still looking for a way to do this, but I too wanted to do it and I've got a work around. In word 2016, btw.
In my case I wanted a heading followed by a blank line, but with information in that line that would appear in a TOC. I didn't want to use white text, because the finalized document is issued as a pdf and the text could be made readable, plus anyone who wants to edit or read the text while they're working is at a loss.
I started with the heading I want to appear along with the bond on Level 7. The text on the next line - which I want hidden - is a heading on level 8. Follow that with a third line, containing only a blank space, which is a heading on a higher (lower, numerically) level that I'm not using for anything else - in this case I used 6. Then change the para mark between the level 8 and level 6 headings to style separator (Ctrl-Alt-Enter), so both level 8 and 6 are on the same line. Follow that with body text.
Then if I collapse the level 7 heading, the level 8 heading disappears. The level 6 heading stops the collapse at the end of that line, so it appears as a blank line between the level 7 heading and body. Then set the TOC to show levels 7 and 8 but don't show level 6.