It has been awhile and I was thinking that this shouldn’t be to difficult and the basic function isn’t!
I created a small function that creates a button for each flexible field on the page and when clicked it toggles the .-collapsed class to the fields. I’ve not tested this in depth, but adding this to your functions.php gives you the basic feature.
https://gist.github.com/mvaneijgen/41fbf1088c5fbc3b948c481cdea93dd8
I’ll be testing this out and if there are any changes I’ll update this gist
