Exchange 2010 and shared mail boxes

Hi

im wondering if anyone can point me in the right direction.
I have multile shared mailboxes in this case 15, we add new users to these mailboxes a few times a week and its long excerise so ideally i want to add a GP that i can add the users to that will give them full access to all 15 mailboxes, This will be instead of adding them individually.

ive been up and down google a few times and non of the solutions seem to fit the purpose,is this type of thing not possible?