The simple answer is to add more sugar. Yeast energizer or nutrient will simply dry it out faster, not make it drier. The real question, however, is why? This stuff will knock you on your rear, regardless. And it has the potential, if too much stronger, to hide the lemon flavor and just come through as ... alcohol.
Beware of adding all the sugar at once - high gravity brews can get stuck. Think of doing a stepped addition to the additional sugar, if need be.
Also, be aware of what yeast you are using, and the tolerance of said yeast.