He doesn't need one. If he thought he could take on NATO he would just attack. Maybe fabricate some shitty justification that's paper thin. "Zelensky is a Nazi" was the best he would bother with for Ukraine, an inseparable Slavic brother nation.

Don't forget pretty much everything Ukraine is using now came from our factories, so this would just be one more thing. I suppose it would be imprudent to advertise it as Ukrainian staffed.