you can grant "send as" without granting mailbox access, but you would need to type or cut/paste the sender into the "from" box each time, and the sent mail would go into the real sender's mailbox, not yours.
to gain access to the settings, go to mmc users and computers snapin, tick the "advanced features" option in the view menu, and you should be able to see a "security" tab in your own user settings. use this to add a "send as" permission for your assistant.
now, on your assistant's copy of outlook, open a new message and select the "options" ribbonbar at the top. the "bcc" and "from" items are in a section marked "fields". select them both.
you can now place your email address in both the "from" and "bcc" fields in the email, and your assistant should do this - that way, the recipient receives the mail as being "from" you and you get to see what it is your assistant is sending on your behalf.
however, in practice I have found it is often easier to set up a copy of outlook express as a separate "send as" mail client. that requires no permissions (unless your local smtp listener needs auth for relay) and keeps a firewall between their/your real email accounts and the fake sending account.
