Well you could try adding it to the secondary and leave it for a long secondary since it will actually be a true "secondary fermentation."
I googled and there's not much mention of adding sugar to the secondary, but that doesn't mean it wouldn't work....
If I were going to do that, I would run the my autosiphon back and forth along the bottom of the fermenter a couple times to make sure I picked up plenty of the yeast to eat the sugar...you'll know if it worked, if you get a krauzen in the secondary in the next couple days....
Then I would make sure to leave the beer alone for at least 3 weeks in the secondary to let everything drop out and clear.