The trick with cold smoking in these units is the fuel. Think small, sawdust or shredded will produce smoke at the lowest temps. Chips will produce smoke but at slightly higher temps than the dust. The on/off method also works. Turn the smoker on until the smoke starts and then turn it off. When the smoke begins to stop, you turn it back on. This is more of a PITA but works for smoking stuff like cheese.
You can also easily create your own cold plate. I use 2 layers of ceramic tile from Home Depot where you can get the tile for a buck each. No need to spend big money on a SI cold plate.