no, Chuck, I add it at the time I actually am making up the burgers. I put in liquid smoke, a good bit of finely grated onion(that releases a lot of liquid into the burger) some food processor-ed portobello mushroom for the same reason, a little dash of worcestershire,a small amount of beef steak fat my grocer does up for me really fine, and a bit of teriyaki baste and glaze...and work the burger loosely.
I don't like overworking the burger meat because it makes it too dense...if you leave the meat somewhat loose, it cooks faster so just work it enough to get it formed into a patty and stop.
Put her on the grill and keep the heat down and take your time cooking them so you don't over cook the outside before they get doneinside..and don't fork em ever- only spatulas here...so the liquid doesnt leak out at all..keep them moist.