First of all, why in the world are you trying to clear a wheat beer? They're supposed to be hazy. It's a characteristic of the style. Wheat ales and stouts are the two styles I don't bother using gelatin with.
That said, the way I use gelatin is directly in the primary, as follows. I move the fermenter into the fridge to cold-crash. A day later, I take 1 cup of cold tap water and sprinkle 1 tbsp of gelatin on top of it. I cover it with sanitized foil and leave it for 20 minutes to "bloom." Then I microwave it - 20 seconds at a time - until the temperature hits 150° F, then stir it to ensure everything is completely dissolved. You don't want to go any higher than that temperature, and certainly don't boil it.
I then just pour it into the (cold) beer and leave it for another 3-4 days before racking to a keg.
