For the cost of a Green Rotating Beacon on or adjacent to the Helideck....and the direct involvement of the HLO to turn it ON at the deck edge...signifying the Deck is ready to receive Aircraft......the problem could be solved.
The failure mode....no light ON....would signify a fouled deck and landing not allowed.....unless directely instructed to do so by the HLO of the Deck immediately prior to landing by the aircraft after visually sighting the aircraft.
That would allow for a failure or the rotating beacon for some reason but would require direct radio communication between the HLO and the aircraft and visual identification of the landing aircraft.
Or am I thinking all wrong here?