I usually do a preseason trip or two to Diamond Head out of Squamish. There are a couple nice pow runs and little pillows and cliffs out there, and it's pretty high elevation so as long as whistler has snow at the roundhouse, there's gonna be snow there too. Most of it is relatively flat though. There's a lodge that you can warm up and eat lunch in too.
It's a full day trip though, because to actually get to anywhere skiable is a 2 hour hike/skin up if I remember right. Nothing better than a day in the mountains before resorts are open. And you can ski the whole way down to the parking lot usually too, so you get a 45 minute run slashing pow turns beside the trail (it's a logging road until the hut).