It still needs to be proven. Our justice system does not require you to prove you're innocent, the prosecution has to prove you are guilty, and that should not change. Better a few guilty go free than the innocent be punished.That would violate our standard of justice, under which the prosecution has to prove you are a straw buyer. So no.
Well, that's why we need stricter liability... YOUR gun was found at a crime scene and oddly, no police report was ever filed it was stolen... um, yeah, it probably means you were a straw buyer.