edit address book cards that have been synced with facebook

I have synced my address book with Facebook, which I love btw.

I have always really enjoyed the birthday calendar feature. I have manually populated the birthday field in address book for my closest family & friends and love that I now have more friends' brithdays displayed.

But my calendar is overwhelmed with ALL my 500 or so facebook contacts' birthdays!

I want to keep some birthdays, but delete most.

When I go into a contact all the data added by facebook is greyed out, I cannot edit, thus cannot delete the birthday field.

Is there a solution to this besides having to manually create calendar events for the birthdays I want to keep and swicthing off the birthday calendar?

Thank you,

Danielle