The auto log-in is based on a cookie on the persons PC. Generally you will not get that cookie until you log in with the check box checked.
You, or whoever, has therefore got to set a cookie at the time of activation that says log in true and auto log in.
I would think that your best solution here would be to request a MOD for this in the MOd request forum. . .
I already did that but many users (dumb?) still can't understand how to do this. I've seen some forums which autologin you after you click the activation link... how to do that?
Not blonde are they? Makes me think of the "If PC users were drivers. . .". Frightening thought. . .
Hope this helps. . .