Yes. Log In to your Snap Shots account, and from the dashboard, click "Edit" for the site for which you want to change this setting. On the "Look & Feel" page, expand the "Advanced Settings" section and make sure the checkbox next to "Enable Snap Shots for External links" is NOT CHECKED (note that this checkbox is different than the "Enable Snap Shots for Internal links"). Then, click the "Save" button.

Then, for each link that you DO want Snap Shots to display, add a 'snap_shots' class. For example: