Redmine

My redmine installation is located in a "secure" network without an access to the internat.
Is there any plugin which allows to change usage of gravatar.com to some local storage of "global avatars"?
Users in this network are not allowed to place any images into the network, so I need gravatars to be assigned automatically. Though it would be relaly good if users could select an image from some list.
Any ideas about this?