A normal AS355 wouldn't be able to hover on one engine above a certain weight - and that weight is not generous (from my 2000hrs on type "F2"). An "N" model is quite alot of grunt again, so the single engine capability is better. As mentioned before, it depends on the day and number of persons onboard.
Secondly it would need to stay outside its dead man's curve (even for twins).
Finally - if it was me running this particulr evolution, I would want to inform and educate the parents about the risk of a helicopter hovering over inhospitable terrain with their loved ones onboard and obtain their 'informed consent' before taking it further.
https://www.youtube.com/watch?v=cDj6oYaYrR8
You see, the problem with doing stunts like this is great if you have Bear Grylls outlook on life. But for Joe/Joanne public - they don't see the risk until their little one has been killed all for the sake of a TV stunt and some Zed list entertainer. Then the law suits start flying and someone gets sacked and the producer of the BBC says sorry in the Times and Bear Grylls skunks off radar for a few months and Mr and Mrs Smith try to understand (for the rest of their lives)where it all went wrong.
Two things in this order:
"Informed Consent" of all participants.
Aircraft Performance.