It's well agreed in the above case that simply coming into ownership of a manuscript, even an original one, does not grant copyright.
Is it legally possible to create a bearer document granting copyright ownership? This would work similarly to bearer paper in other contexts, such as stock. The person who legally owned the bearer paper would automatically become the owner of the included copyright.
For example, suppose I write a novel that I never publish, instead stuffing it under my bed. I write out and sign a bearer deed granting copyright in the work to whomever legally owns the deed, and then slip it under the pillow of my favorite niece on her 18th birthday. When I die, my son argues in court that the transfer of copyright by bearer deed is "unrecognized in law and entirely null and void" and asks the court to subject the copyright to probate as part of my estate. Is there any precedent to indicate what would likely happen?
To be clear, this question does not cover theft in any way. Ordinary bearer paper (e.g. bearer checks, bearer stock certificates) do not grant ownership to persons who have stolen the certificates, but only to their legitimate owners. What would happen if someone physically stole/sticky fingered/yoinked, etc. the bearer deed to the copyright of my novel is out of scope.