I've smoked fish on mine, just propped the door open with a small piece of wood until i achieved the temps i was after. Not ideal but it got the job done.
Ha maybe i should have read your entire post... no i have not tried the add on. But somebody on here fashioned up a dryer hose from the exhaust on their traeger to dump into their gas grill and cold smoked that way.
You'd think there has to be a simple way to manufacture a little extension on the stack and make a little cold smokehouse for doing cheeses and such. If someone has done this, please share it. For cold smoking I just use my Cookshack.