The owner of the plate could definitely transfer it to another car or onto a retention document. I don't know whether they could transfer it to you, though I think they should be able to.

http://www.dvla.gov.uk/faq/faq_transfering.htm
http://www.dvla.gov.uk/vehicles/cherish.htm

Unfortunately nothing on the DVLA website seems to lay out the exact rules and most of the forms aren't available to download. It might be easier just to call them and ask.