no username placeholder on welcome email

[tosione]

I register my users as Admin, an they get the welcome customized email with the login data.
I want to send them their username, but there is no placeholder for their username like the email has [email] or password has [password].

I tried [user], [username], [myuser] and others but none worked.

I know that that the email is enough for login, but I still want them to know their username.