Toolbar - Single use operator with a fallback toggle to another tool (act once clickable buttons in toolbar)

I’ve been trying to make addons with operators that add buttons to the new Blender 2.8 toolbar, but concerning UX, the new buttons should work like a clickable button. eg, an operator from the header menu (click once, act once, default to normal/former tool again). But every time I try make a tool in the toolbar, it creates a “mode” where the tool remains active and acts again and again on every click, with no way to turn it off till I switch tools deliberately - all I want it to do is act once, then fall back to the default/fomer tweak tool or something else (like the way the rest of the UI work when using an operator that isn’t in the toolbar).

Q. How do you make press once operator buttons in the toolbar?

Reason: I want to expose some header operators and addon operators to the toolbar for quick mouseover, but keep their “act once” clickability (not have them as “active tools”). Is this possible?