One way – You could use the CSS “: / ::before” psuedo element along with the “content:” property on the “navbar-toggle” class by adding it via the Page Settings > Add Code.
Then adjust the style however you want based upon the hamburger symbol you choose, site design, etc. Here is a quick example when used along side the “standard hamburger” symbol, including some various CSS properties to begin playing around with.
EDIT: Here is the CSS from the above screenshot:
font-family: 'Lato', sans-serif;
I’m not really saying you need all these properties, you may need others or fewer. Its simply a starting point to begin exploring this method based upon what you want to do with your design. With “:/::before + content:” you can also include icons, images and do many other things.
So explore and have fun. : / :: )
Otherwise I think @norm could probably add something in the app with setting(s) in the sidebar for toggling such a features use and input parameters. The next version of Blocs may already provide opportunities for other more direct approaches also?