You can't.
The only way to fake the owner is to use the suexec command in
Gerrit's SSH daemon to become another user, and execute `git
receive-pack PROJECT.git` as the command. You can specify the command
line from the client with `git push --receive-pack="suexec ... "`.
There are issues with using suexec, like the end-user must login as
"Gerrit Code Review" and must present an SSH key that is on a special
authorized keys list that grants super-Administrator privileges.