General :: Change Umask For Files Created In Ext2/ext3

I have ext3 partition mounted on /mnt/shared/ as follows

Code:

Permissions above are of the actual mounted fs.

Goal is to have all files created on the fs
1) to belong to group 'users'
2) to have this groups permissions set to rw (rwx for directories) so that all users who belong to group 'users' have full read/write access to data and everyone else to have only read access.

Now because of setgid bit (s) in group permissions every file created has group 'users' and additionally setgid bit is set for directories. Because every users umask by default (on my system) is set to 0022 all created files will have permissions 644 for ordinary files and 755 for directories.

Net result of above means that users A and B who both belong to group 'users' won't be able to modify files created by the other.

So how can I make files created on the fs to be created always with umask 0002 WITHOUT changing default umask for users that is used elsewhere (like in their home directory) ?