just add an custom icon to the file itself:
Customizing icons under Mac OS X is straightforward. Simply click on
the icon you would like to use and select 'Get Info' from the 'File'
menu. In the window that pops up, click on the icon and select 'Copy'
from the 'Edit' menu. Now close the info window, click on the icon you
would like to change and again select 'Get Info' from the 'File' menu.
Click on the icon inside the info window that appears and select
'Paste' from the 'Edit' menu. Close the info window and you are
finished. (taken from the interfacelift.com FAQ)
