You have the right idea prefixing the event with 'me', but you have forgotten to at the user level to the beginning of the event as well.

Code:
alias ident-esper .msg nickserv identify <password-entered-here>
on me:[color:blue]*:[/color]NICK: if ($me == <nickname>) && ($network == EsperNet) { ident-esper }


Add the section in blue and it should work.

- Jason