Timed Gaze Input selection trigger for Cardboard?

In a previous project (using Oculus / Unity native VR), I custom-created a gaze-based selection system (ie. a timer is triggered upon entering a raycast collision, and an animated icon shows when the event will trigger if you keep looking at that object); however, it did not use UI / EventSystem / etc.

I'm trying to implement the same sort of setup for Cardboard, but finding it a little cumbersome to trace through all of the different references and instantiations to find where I would...

Timed Gaze Input selection trigger for Cardboard?