Repitching is a reasonable idea. You may not have to though. Sometimes you get fermentation without a lot of drama. Recheck your gravity in a couple days. If it hasn't moved then you may want to repitch.
If your going to repitch I'd make up a nice starter with something close to your original sugar mix. Aim for about 1.03, or a little lower, on the gravity. The point is to give the yeast food, not produce alcohol in a starter. I'd do about a quart for the starter. Also include the total amount of yeast nutrient and yeast energizer you would normally add to a whole batch this size. Since you've already got alcohol present in your brew you'll want fermentation to have passed peak and be about done in the starter before adding to your brew. That way the yeast will have had a chance to develop nice tough cell walls as they prepare to take a nap. That's usually 2-3 days for a nutrient rich starter like that.
In any event, enjoy some sweet beer.
EDIT: You could also use another yeast type for the starter. Champagne yeast comes to mind. It's got a fairly high alcohol tolerance and has a tendency to chomp sugars that most other yeasts usually leave alone.