There's plenty of sugars left in there that you shouldn't need to add juice, but it wouldn't hurt if you have headspace in your fermenter. (just keep in mind it will increase your ABV, alter your Gravity Readings and Prolong Fermentation)
I've never used it, but I've heard some people add yeast energizer to kick up a slow fermentation.
If it looks like it's still moving, I'd let it ride for a while. If it drops to 1.005 or below, you'll definitely have enough yeast cells to bottle.