make user avatar default if site avatar isnt uploaded

Hi, So here's the issue I am running a multisite install and the issue is with the plugins Avatars and the Blog Directory. Both are working fine the only issue is that some users will upload a user Avatar but not a site Avatar. What this means is that most blog directory Avatars are set to the mystery man default. My question is this. Is there a way to make the user Avatar the default Site Avatar if the user doesnt upload a site Avatar?
Thanks
Meriam