Not possible again as posting preference in options were removed.
This is now possible.
No this is not possible.
This how the admin setup works, you are basically taking up the PR role of the page so the face should be the brand.
Pages are for organizations, businesses, celebrities, and bands to broadcast great information in an official, public manner to people who choose to connect with them.
Please note that only the official representative of an organization, business, celebrity, or band is permitted to create a Page.(1)
(1) What is a Facebook Page ?
The way I used do it, is similar to Twitter signatures, appending my initials at the end ^PH .
Send your name to Mars (NASA) ^PH
I also added a FBML tab with the faces of all those who are admins along with initials.
If you dont like this way then you should have only one person who stays as admin and you all send him posts via email/chat/etc. That way the rest of you can just be regular subscribers of the page.
Otherwise you may just want to look at Facebook Groups.