No brainer
EEDSL is correct and for once I agree with his points!
EC155 cost new 10M Euros, that's worth noting:
The pilot of this must have an IR, no ifs buts maybes.
He should have a co-piot, type rated and also with an IR
Annual cost of both: Captain £70k co-Jo £50k
If the above are not in the budget make it so or send the boss the last twenty corporate Heli crash reports from around the world. Yes two pilots can make errors and hit terrain but most of the time the dead rich man was being flown by a single pilot, or himself.
I have flown S76, Dauphin EC155 and lots of smaller things; To date, with 10,000 plus hours I've had a few good bird strikes, one even came in and joined me, I've had several near misses, even with TCAS, I have not had my heart stop yet but others have, I've gone 180 degrees wrong on an approach but lived, and flown 1000ft too low over terrain reading a chart over the alps at night when diverted through weather. All on my own, others haven't been so lucky.
Even if your pilot is the most ace of aces, and I doubt it very much if he doesn't think he needs an IR, then many other factors can strike down the lone driver. That is a risk you take with smaller ops but if your owner is worth more than a few million there is no excuse.