project 'trac' directory write access to the project group

Hello.

As I see, all the file system content of project directories has the group owner named after the project name. 
Except for the 'trac' subdirectory, which has group owner = 'www-data'.

For example:

# cd /project/cl-openid
# ls -l

total 16
drwxrwsr-x  3 mpasternacki cl-openid 4096 Jun  5 04:55 cvsroot
lrwxrwxrwx  1 postfix      cl-openid   30 Sep 24  2008 ftp -> /var/ftp/pub/project/cl-openid
drwxrwsr-x  4 mpasternacki cl-openid 4096 Aug 16 12:59 public_html
drwxrwsr-x  7 mpasternacki cl-openid 4096 May  5  2008 svn
drwxrwsr-x 10 mpasternacki www-data  4096 May 16  2008 trac

In result, the project members other than the directory owner can't use trac-admin or
edit trac.ini.

Is there a way to overcome this, other than every time assigning the user owner of the 
'trac' directory to the project member desiring to change the files?

I assume we can't just change the group owner to cl-openid here, because www-data
needs write access to 'trac' directory (when the trac python code tries to save something
there).

Best regards,
- Anton