This feature was added in v3.7 and is found under in5 > Interactive Widgets > Fixed Position Element.
The Menu Builder (in5 > Build Wizards) can be used to easily create a hamburger (compact) menu.
Hi, I've updated the answer above. This feature does exist now. It can be used to pin an item to the top right of the browser window. If you use Desktop Scaling set to Fit to Width, the browser window and the document will share the same upper right corner.
Hope that helps!