Had a similar issue in our group where a new member did not yet have a PPL (although obtained his PPL very shortly after buying his share).
Our insurers advised that adding a pilot with less than 100 hours (but with a PPL) would increase premiums by about 10% but that a pre-PPL pilot would result in an "astronomical" increase.
With the agreement of the individual involved, he did not command the aircraft (or receive instruction in it) until he had his PPL. He also reimbursed the group for the additional 10% premium.
Obviously every insurer and group will be different - would be worth discussing the options in detail with your broker.
As a sidenote to this, the new member in question at the time had 55 hours in a Cessna 152 and about 65 hours in a CTLS aircraft. Picture both side by side and compare the performance - most would say they are pretty comparable and even that the CTLS took more skill to fly. However, his CTLS time did not count towards the 100 hour minimum as the insurers did not consider it to be "fixed wing piston" time...............
