I'm not aware of any wired switch that uses a single wire to control the fan and light individually. However, you can purchase wireless remote kits to retrofit an existing ceiling fan. The receiver is installed in the canopy at the ceiling, and it has separate leads for the motor and light. Then you use the remote control for both fan & light, and you don't have to do anything with the wall switch but leave it turned on.
I've seen these kits at Lowe's and Home Depot.
The fan in my house came with the wireless remote and I love it. The remote almost never leaves its holster on the wall, but that's OK. It works great.
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.