[rcarr]

I believe you might be able to replicate the functionality using BetterTouchTool but it might be a bit of hassle to do, not 100% sure though.

[037]

You are right, but it’s not very difficult:

The trigger can be “Double-click Main Menubar” and the action “Show / Hide Menu Bar Icons left of the BTT Icon.”

You can even add actions to hide them again after a certain number of seconds or minutes.

(It’s only a partial replication because Bartender can show you the additional icons in a secondary bar, if needed).