Um, why do you want to do that? You won't be making the same beer if you do that. Sugar in Belgian beers has very specific reasons for being in the beer, like it is for most high gravity brews, to dry the beer out and contribute to the 'higher gravity without boosting the body to the point that grain does. Look at it this way, what is the difference between a barleywine and a Belgian Quad? They're both roughly the same gravity, but the body is different. Belgian beers, no mater how high grav tend to be somewhat thinner in body, and less filling than a barleywine.
You need sugar if you are trying to be true to style.
This isn't some of that "I read that adding sugar in my beer is bad" nonsense, is it?