No you can’t. This is the defining attribute of a Rossi believer, namely that they think evidence is required to contend that something does not exist. The only possible evidence for lack of existence is the absence of evidence of existence. Rossi believers appear to have a defective logic gene that does not permit them to understand this.
I'm torn between evidence of the absence of evidence of existence, and evidence of the absence of evidence of non existence.
Surely there is a vaccine for this.