@Martine: yes you must basically have it right. A similar arrangement, that went wrong in a not very impressive manner, is described in the below reference, though here the "relay" was to be a helicopter too.
http://mobilit.belgium.be/nl/binarie...466-209194.pdf
And no, I think few helicopters carry ADS-B so you wouldn't see them on flightradar24 et al. As they generally fly quite low they wouldn't be very visible anyway.