Think they better look for a boat, nearest land I think would be St Kilda but that would be still a 330 NM round trip (not sure but think an EC225 or maybe an S92 could do this ) but not much of a landing area on Rockall.
Maybe the combination of a boat with a helicopter on it would be the best of both worlds. They would need deep pockets to pay for such an expedition unless they get Mr Abramovich to sponsor & loan them one of his fleet.