[Samba] username map before passwd?

[Häfliger Peter]

Im using Samba 3.0.14a.

My problem is, that smb starts username mapping before it looks in passwd.
last line of username map looks like follow

###
domainuu= mars\*
###

if user not exists in local passwd, so it should be mappd to domainuu (works fine)
but if i connect as user mars\peter (peter exists as local unix account) it is also mapped to domainuu. 
but should connect as user peter.

is there any parameter which i can say, it should first check /etc/passwd and afterwards username mapping.
otherwise i need to map every local user in username map like follow

###
!peter = mars\peter		<- ! match stopps further mapping
domainuu= mars\*
***

The thing is, i need to map every domainuser (mars) to domainuu, to use domainuu (unix user) as public share like domain guests.

ps: security is domain

thanks for any help

Peter