You don't really want to add irish moss to the cold keg. Gelatin would be a much better choice at this point. Grab a packet of unflavored gelatin from the grocery store and dump about 1/2 of that puppy in there. It'll coagulate the proteins in about 24-36 hours. Just remember that your first pour is going to have alot of solids, so just dump that first pour.
BTW, you may just have a chill haze to your beer at this point. Even with irish moss in the boil, the beer needs about 10-14 days at serving temps before the chill haze starts to clear, so you may just want to be patient and this one will clear up. If you don't want to wait, do the gelatin!
Good luck!