If you don't want to use a blowoff tube, you can just loosely cover the fermenter with foil/paper towel/whatever if it's a carboy or leave the lid loose if it's a bucket.
Also, I just looked at the recipe, and I would absolutely, 100%, no doubt in my mind, leave out the maltodextrin - even replace it with sugar if you want. In a tripel, that's just bizarre.