Keep the fats as cold as possible before you start. Done right, it will more than compensate for the warmth of hands, blender/processor parts, and ambient temperature.
Having somewhat chilled your choice of fats, separate them into small, 1 inch sized pieces, working with copious flour to keep them from sticking to one another. Place this in the freezer overnight. This allows the blade to chew up even near-frozen bits. I haven’t noticed much degradation with this method, though I wouldn’t the leave fats in for much longer than that.
Mix your dry ingredients together.
Put the thoroughly chilled fats in a blender/mixer, leaving some room. Then, using only as much dry ingredients as necessary, pulse the fats until you have pearls slightly smaller than fish gravel. This works especially good for blenders where the ingredients tend to get stuck at the bottom. If you get the chance, stow the blended stuff in the freezer while you work with the next batch.
Once you have completed the blending en masse, you can add the rest of the dry ingredients. You should have a uniform texture to the whole mixture. Add water until the dough comes together with limited kneading. Wrap and return to fridge as soon as possible.