I'll give you a few idea's
1. If the switch's control outlets that say lamps are plugged into, you could use lamp modules at the plugs.
2. You could remove the box from the wall, cut the hole in the shreetrock larger and install an old work 2 gang box, then install 2 standard size switch's
3. There are x-10 modules that can be wired between a lamp and power source.
4. You could remove the existing switch, replace it with a standard size and then use another means of control for the second circuit, you could add a second box with switch, or an inline module.
I'm sure there are many other ways to do it, much of it comes down to how much work you are willing to put in and your budget.
If you contact Bill at
http://www.homeautomationnet.com/ he can provide you with any products or info that you might need.