agreed. adding sugar mid fermentation is traditional in these big belgian beers. I do it with both my quad and tripel.
Just make a quick syrup from the sugar (1lb of sugar to 1 cup of water is pretty standard I think). Cool, and add once fermentation is past 50% (aka, shows the slightest signs of slowing down).
Primary 1:NE IPA Style Saison
Primary 2: Raspberry Wheat
Primary 3: Typical Pale Ale
Up next: Lemon and Thyme Blonde