Hey djaydino,
I indeed found a custom action for Mouse Pick Event, thanks.
No such luck for UIOnPointer events...
I ended up going with a different solution that seems to work for everything. When I need events for the overlay camera I send an action that changes the tags for overlay camera to 'main camera', and main camera to 'untagged'. When I need events for main camera I send an action that switches the tags back.
Luckily the need for events for each camera arise at separate times in my game (character switches on/off a notebook, everything in the background is blurred/unblurred accordingly). But if I would need them both at the same time, not sure what I'd do...