The slow way that works:
Mage::getModel('catalog/product') ->load($productId) ->setStoreId($storeId) ->setData($code , null) ->save();
Mage::getModel('catalog/product') ->addAttributeUpdate($code, null , $storeId);
This however deletes the default value as well. (possible bug ?)
Other examples I have seen are raw mysql delete queries.
I though that this would be something native to Magento.
Any thoughts on this?