There is a non-official way of doing this. This means: not documented, not tested, and no support for it.
You can still try it, “at your own risks”:
Enter, in file:
AppData\Roaming\Steinberg\WaveLab 8.5\Startup.ini
the additional line:
canMulti=true
With this option, you can start more than one instance.
Obviously, you can’t use the same audio i/o device in both instances. And since settings are shared between WaveLab options, this won’t be practical.