You might get them to mount to a door jamb switch box, but I don't think that will CYA with UL listings
. Many European luminaires are designed to be mounted to hooks on plaster walls or ceilings without any kind of box and simply won't match up to anything we have here (one of the dubious benefits of so much wood frame construction...). There aren't any boxes available in Europe that would have mounting options for these luminaires. Most boxes are plastic and are only designed to be embedded in plaster for device mounting.
One way to handle this that I've seen is to convert the sconce to 12V and use a Class 2 transformer. You'll likely need socket adapters from the European size to candelabra, and candelabra base 12V lamps. Is it a completely NEC compliant method? No, but it does seem like a safe compromise and can be done very neatly and in a professional looking manner. Responsibility would be on you.