Ref: My original posting
I have done some considerable research and I have even talked to a few relatively high-powered people over at Stack Exchange about this and the consensus of opinion is that this isn’t doable - at least not with the current tools.
However, there is also a consensus of opinion both in posts here as well as there that the ability for the gamepad API to fire an event when something happens would be a valuable addition, and would expand the gamepad API’s utility beyond shoot-em-up’s on the browser. (wink!)
What is the correct method for proposing an enhancement request to whomever runs that particular show - the gamepad API?