You can now enable / disable direct linking at the account level and the gallery level.
You can edit your direct linking setting for your whole account on your account page.
Then, on the advanced view of the edit gallery page, you can choose to accept or override the account default setting just for that particular gallery.
To get to the advanced view, just edit the gallery and click the 'advanced' link near the top of the page.
So, if you only have one gallery of images for which you want direct linking enabled, you can disable direct linking on your account and then enable it for that particular gallery.
Enjoy!
-Emily