I want to visualize some data on the background of the Gnome Shell top panel, behind all of the other elements. Like in this mockup: https://i.stack.imgur.com/tv1aH.jpg
Playing around with other extensions and reading through the St API docs [2] I found no obvious way to do something like this. The only elements in Main.panel that have insert functions (e.g. _insert_child_at_index) are _leftBox and _rightBox, but that's not what I want since I want my visualization to be behind the other elements, not next to them.
Ideally, I'd like to dynamically add/remove and absolutely position elements anywhere inside Main.panel (or behind it if that's possible), without affecting any of the existing elements.