We already have private citizen volunteers in Ukraine and recruiting of ground troopers is as public as the doorway to the Ukrainian permanent mission to the UN (saw this last week when I was in NYC) where you can apply to go fight or donate to the Ukrainian MOD.
So, yeah a squadron of western nuclear-capable fighter bombers might be a bit scary for the policy people. I totally get that. But, paint them yellow and blue and just tell Russia that they exist and to suck on that.