Before I do a packer, I will most always PARTIALLY split the flat from the point - makes it much easier to separate after cooking, especially if I'm cooking it for someone else that's not particularly experienced in separating the two muscles.
Now if I have a particularly large brisket, say 16 lb or over, or one that's just longer than usual, I will completely separate the point from the flat, and lay them down together on the grate in their same original configuration, just lapped over a little more than they were to save a few inches. I may also set the two pieces at a bit of an angle if I need to, in order to get them to fit better on the grate. Thus the benefits of cooking flat and point together are retained, and the size issue is solved. Even though they're stacked on top of each other, though, they WILL cook faster than a solid packer, so watch your temp and your "waba-waba"s. Better yet, ignore the numbers on your thermometer, and when the thermo probe slides into the meat like it was sliding into soft ice cream, and you can't tell if you're sliding into lean or a fat pocket, wrap that puppy up in a few layers of foil and throw it in a dry ice chest for a few hours to have a nice nap, and prepare your taste buds.
I always keep the hard fat trimmings to tuck under the ends of the brisket to catch the brunt of the heat coming around the edges of the waterpans. You still get the tasty burnt ends, but you avoid BURNT ends, if you follow me...
Keri C