I have some questions about the context...
If it is a "kitted" product, are you going to be selling 2 configurations? IE, one for US use (item A (CE marked) and item B (not CE marked)) and one for EU (item A only)? Or are you adding an item to the kit with the intent to start distributing now in the US and not distribute in the EU until it is approved? If you are selling 2 configurations in the meantime I would just avoid the issue by providing separate IFUs (since presumably you already have one that is specific to the CE marked product).
But to answer the question you actually asked:
I would use language such as "Products depicted may not be available for sale in your region. Contact your sales representative or distributor for more information on the products available in your area" (I would put this in the "introduction" or near any pictures/diagrams of the product).
You could also add an asterisk and footnote that states "Not CE marked" or "Not available in the EU" or "For US use only" or whatever makes sense.
Near the CE mark I would add something like "CE mark is only valid if found on the product label. Always refer to the device label for CE mark status".
You don't have to worry about someone taking a product somewhere else and using it there if it's their personal property. The Regulation is primarily concerned with "placing on the market" and "putting into service" which would not really apply for someone who has legally purchased a device for their own use.
