You don't need a protocol change to do that if it's already possible to put your information in it.
Just change the extra information to
your name + previous block hash you've mined + sign(your name + previous block hash)
It should be possible to not insert this information so real anonymous mining stays possible.
That won't work but I wasn't suggesting a breaking protocol change but rather an agreed upon optional standard which is fully backwards compatible.
Instead something like pools (optionally) create a public private keypair used for signing (probably should have mechanism for revocation or replacement).
The pool would modify the getwork so that they hash some standardized identifer (should be specific to the block to avoid substitution attack) and sign it.
Yes I was indicating such a system should be optional but sites like blockchain.info could scan the block look for a signature and then verify it w/ the pool's public key. In cases where the block can't be verified (or no signature is present) blockchain.info and other sites could still try to guestimate the origin by IP address. As long as the signature is placed somewhere which isn't a breaking change uniformed clients would simply ignore it.