I want to be able to install a web app with a umask of 0002 rather than the default 0022. I have worked out how to get the www-data user to have a umask of 0002 when used by apache but I'm not sure how to *install* the app with the required permissions.

It's being installed and kept up to date by using the standard apt in Ubuntu (it's on a PPA). Does anyone know if it's possible to tell apt to use a different umask? I.e. if I set the umask when installing will I get the effect that I want or does an application installed by apt set its permissions by configuration somewhere?