You are correct Kmax,
So long as you only want to fly EASA reg G650, you are fine. I think you will have a big problem if you want a FAA type later on, since it would be a mountain of paperwork. I bet you will have to take the entire initial over since FSI would otherwise have to get approval for a new variation of "upgrade" type,,,, (if you ever deal with training organizations and the feds, you know how difficult it is).
So I'd say to bite the bullet, and sit through the extra few days in class and get the whole thing. I bet they put you through a full initial anyway, but give you days off when teaching the redundant classes... And it certainly won't cost more...
FR