On paper, its a simple challenge: Napoleon still attacks Russia on schedule, and wins. You even can be flexible with your definition of winning. So long as its historically regarded as a French victory, it gets my stamp of approval.
Possible ideas to incorporate:
- Don’t go chasing after the Russian army once it becomes obvious they’re dedicated to scorched earth tactics.
- Don’t try to win in one year’s campaign. Be willing to winter in a well-supplied and secure winter base.
- More actively support nationalist revolts, such as among the Lithuanians and Balts.
- Free the serfs.