If you're a one man band kind of studio operator.... the bigger question is why would you want to do that? You have the ability to multi-track one track at a time, so why not do that?

In a live stage rig, again, to do that, you would need to have a keyboard that allows you to split the keyboard and assign the outputs accordingly. I'm not personally aware of any VSTi synths that have the ability to have multiple channels in one synth except perhaps TTS. Most of the better ones are all one channel synths. At least the ones I have are that way. You could always run 2 instances and make it work assuming you can split the outputs properly.

You can find my music at:
www.herbhartley.com
Add nothing that adds nothing to the music.
You can make excuses or you can make progress but not both.

The magic you are looking for is in the work you are avoiding.