He could have made a deal with Ukraine, similar to what he did with Slovakia. Basically a puppet state but pretty much leaving the Ukrainians alone, and even allowing them to exact revenge on the Russians. Most Ukrainians would have welcomed it.
Yes, I have always believed that if the Germans had entered as liberators rather than as oppressors even worse than Stalin and his apparatchiks it would have been a much different story. But the Nazis saw the Ukrainians and Belorussians and Latvians-Lithuanians-Estonians as untermenschen. Some of them would be spared to work as slave laborers; the rest were expendable, useless mouths to feed. Their land was the lebensraum that Hitler defined in Mein Kampf.