Hello again
You said it... They are all single pilot certified. Personally, on an extended over water flight I'd rather have a life raft in/ in place of the right hand seat in a single piston than a 'student' ferry pilot. In a turbine twin, no problem as long as the insurance firm did not stipulate operating crew only.
You have no need to clarify that the low hours guy/ girl would indeed not be the PIC in a single pilot King Air. I know the insurance requirements for the B200 in our fleet. There is no such thing as a co-pilot on a single pilot aircraft. An "optional" co-pilot would not form part of any insurance requirement, but you may well find that passengers (which you would most probably be deemed in a single pilot aircraft) are not permissable on such flights.
Why don't you contact people in the business directly? There are a few on here. FerrypilotDK flys King Airs across the pond.
Where is your local airfield?
Good luck.