You can't do that, it's impossible.

You'd have to go with something like "show that the massive decline in the Jewish population of Nazi Germany was by means other than genocide".

Which is also impossible, but due to truth instead of poor epistemology.

Ehhhh, you're "not even" allowed to investigate it, so this one doesn't really work

This is false. I personally know academics who study genocide who do serious research on the Holocaust in Europe.

It's just that these people are dingbats who have decided ahead of time to deny the Holocaust and desperately search for any shred of broken evidence for this claim.