While implementing such a thing would be very tricky, I agree with zzmzzm that accounting for Germany's critical oil situation might help with balance. Barbarossa had to happen in 1941 or there wouldn't be another chance for offensive operations on that scale since Germany were projected to be out of oil by Fall of 1941. Perhaps a German failure to take Grozny and Maikop in 1941 or early 1942 should result in a movement penalty for mechanized units and a reduction in supply. I'm talking to you, Rommel and Von Manstein!
On the flip side, if the German player can interdict the Volga by taking Astrakhan or Stalingrad then that interruption of oil flow should have a highly negative effect on the Soviet economy. Maybe having supplied units on either side of the Volga would be enough to choke off the Soviet oil supply.
Some food for thought is Marshal Timoschenko's secret speech to the Supreme Defense council in November of 1941:
"If Germany succeeds in taking Moscow, that is obviously a grave disappointment for us, but it by no means disrupts our grand strategy. Germany would gain accommodation but that alone will not win the war. The only thing that matters is oil. As we remember, Germany kept harping on her own urgent oil problems in her economic bargaining with us from 1939 to 1941. So we have to do all we can to (a) make Germany increase her oil consumption and (b) to keep German armies out of the Caucusus."