Certainly in the UK it is possible to assign any/all rights (including copyright) over to another individual, the only stipulation is that it has to be in writing and agreed by both parties. So a clearly laid out contract that included an appropriate clause transferring ownership of rights would be enforceable.
As a photographer I would be happy to sign such a contract at the right price, but I've yet to deal with a client that was prepared to pay that price. So far all my clients have been happy with a negotiated set of rights that fit their purpose. Why would the client want to pay for more rights than than they actually need?
Cheers,
Ady