I am not sure if I understand this request clearly, or it can actually work.
Router 1 in customer 1 network is in BGP AS 1 and Router 2 in customer 2 network in BGP AS 2. They want to peer Router 1 to Router 2, but they don't want them to be EBGP peers, since Customer 1 acquired customer 2.
Please kindly advise. Thanks.