But that wouldn't prove anything other than that they'd sent themselves a letter/package on such and such a date. It would prove nothing about the contents of the package (which is what they're trying to protect). That's why the Bodleian/British Library thing is/was used - as then they can point to the Library Catalog to establish it existed from at least that time (that it was catalogued)
The government recommends you do what Sussex suggested - post it to yourself. You can get a soliciter to keep the document/material for you or put it in a bank deposit box (which is essentially like the library idea) but this probably wouldn't be any benefit when trying to prove original works in court.
Anyhoo, I can't believe the thread went this far:
You can't copy
write a name (does this word even exist?) and you can't copyright a name.
You can trademark a name: refer to the Elvis Presley v Sid Shaw case.