Is there a mode that lets me set P and A?

Personally, I can't see the problem with manually selecting ISO in manual mode. Is it really so difficult? After all, you've already set aperture and shutter speed - you're only one setting away!

Once you've set the ISO so the shot is properly exposed then that would be pretty much what Auto ISO would have set for you anyway.

I concede that in constantly changing lighting conditions, Auto ISO could be useful in Manual where aperture and shutter speed were critical, but such conditions are surely rare.