I do partial boils as well and I usually chill mine in a sink full of cold water until it gets down into the 80F range and then chill it the rest of the way down with bottled water that's been in the fridge. It works well, but I don't think you're going to get it down to pitching temp with cold water alone.
To chill in the sink, just put the stopper in, set your kettle in there and fill the sink up with cold water. Don't go much past the height of the wort in your kettle though or it'll start to float and could tip. Stir the wort now and then as well as the water in the sink (different spoons of course) and it'll cool much faster. You'll have to change out the water several times as it'll warm up quick. The first time you fill the sink, it'll probably be hot and need to be changed by the time you get it filled. A second set of hands are useful so you can lift up the kettle while someone else reaches under and pulls the plug on the drain.