Unless it is cold outside, I've not been able to get my Traeger to do cold smoke successfully - in my area I always seem to develop cheese-sicles, so I switched to the Bradley, which is famous for low temperature smoking. The problem With the Bradley in the height of summer is that it is still too hot, and the same cheese-sicle still develop.
NepaSmoker posted a technique for the Bradley in which he separated the smoke generator from the main tower - worked perfectly for me and decreased the tower temperature by 20F.
However, I have also tried the ice cube trick which unfortunately left condensation on my cheese - a solution is to freeze water in a sealed container before adding to the smoker. That way you have the benefits of adding cold without adding moisture.