You could go a million paths on this.
If you have some of the same Belgian Candi Sugar you used in the recipe, you could prime with that, I think you'd need a slightly higher amount than normal cane sugar due to some of the caramelized sugars. It is going to be slightly more difficult to evenly mix this in.
You could use some honey, though, it probably won't really contribute any flavors/aromas that could be noticed in a big quad.
Could go freaky and prime with maple syrup/brown sugar/agave nectar/cherry concentrate/apple concentrate/assorted fruit concentrates. Though all of these, except for maybe the agave nectar, will probably change the general profile of the beer. I used a sour cherry concentrate, thick and syrupy, that was about 2/3rds by weight sugar, so as an example you would have to use 30% more of it by weight than regular table sugar.
I would personally just go straight up and prime with invert sugar/corn sugar though to make sure you get the carbonation just right. Big Belgians rely so much on the carbonation being perfect, otherwise they're acidic fizz bombs that blow up the bottles, or theyre thick and alcoholic sweet syrup. If you wanted to get creative with priming, I would only do it with a portion of your total batch, maybe only pull 1-2 gallons off and prime them with something fancy.