Depending on the doctrines the OKW player has available, Luftwaffe supply or Assault Support to augment his fuel income would be very useful.
I can recommend anything that gives you a solid early game presence to secure your place on the battlefield, which greatly augments Kubelwagen plays. Mechanised Assault could work for this but don't spam Assault Grenadiers, they really aren't very powerful when they have nothing to back them up.
Another option is something like CAS to deal with large infantry blobs, massing LMG grens to compensate for his weak infantry as well as dealing with enemy howitzers that pose a serious threat to him.
That's all I can think of now.
