That's an interesting use case. I have submitted this as a feature request for you.
While you can't do that, at present, I'd suggest to try this workaround (note, this method isn't UX/UI wise, but aesthetically will do:
1. Add elements upside down.
2. Change the layout setting of your Navigation bar from Horizontal to Vertical.
3. Next, set the Header background color to transparent from Background Settings.
4. And finally, enable the 'Fix Header' option from Header Settings → Header Position. The latter one, will give sticky navigation bar effect on scroll.
P.S. You will surely be updated when your request is reviewed. Also, feel free to add additional details in the discussion section so our Product team knows how this feature would help you.
Thanks again for the feedback and have an awesome Wednesday.