To sum up JimEli's response: DON'T TRY IT!
An inadvertant transient excursion into less than 1.0 g, due, for example, to turbulence, may be OK, but most helicopters were not designed for less than 1.0 g.
If you think you have a genuine need (?) to be in this flight regime, then ask the Design Authority /OEM for advice and clarification of the flight envelope. Designers and test pilots do their best to give you the widest possible operating envelope: if what you want ain't there, we probably thought there was a good reason.