Well, I'm not sure what you mean exactly, but I guess you can put everything—including the virtualization software—into an external hard disk that you plug into the computer you want to run it on. The problem is that not all processors support virtualization, so you may find yourself unable to demo your software on certain computers.
It's actually really interesting and can really useful. I suppose you can't do that because the whole drivers thing, but who knows.
In any case if the whole purpose is the virus removal thing than why you don't connect it as external driver and check it.
If you want to make your computer absolutely safe, run your computer with BartPE or Hiren's CD and then check it easily.
I use Hiren's CD, but I was just interested in it on a whole. If the drivers are incorrect the system would still run, just wouldn't have the same functionality.
I'm looking for a way to run an external hard drive like a virtual image in a virtualization program, or if there is some way to create an virtual image from a hard drive that can be run, that would work.