We're a family of 5 who'd like to book a 6 berth Artesia couchette from Paris-Venice. We'd prefer to not have to share the cabin (and I assume most single travellers would rather not share with us!). Can we book (and pay for) an extra (non-existent) child as our 6th passenger, so that the bunk isn't allocated to anyone else? Or is this likely to cause a problem when we board? Thanks.