If you were going to try playing with 7 players...?

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Here's some ideas. They all need some kind of dot scoring though. Depending on what you use you may need to add a couple options since an extra hero is worth 5 dots.

2 command pts per player
Increased hand size - 4 cards per player
Improved draw - Draw 2 cards instead of 1 when using the command console
Faster Saucers - Saucers move 3 spaces instead of 2
Start the game with the Martian Leader
Start the game with the Zard Beast
Improved Ray Guns - Ray Guns hit on 4+ or 3+ if full pack
Improved Ray Guns 2 - Increased range on Ray gun attacks
Mind controlled Heroes - Some kind of spin on Zombie Heroes
Cloaked - Martians ignore wounds on a d6 roll of 4+ (except fires and explosives)
Scouts - Martians move 2 spaces each turn
Tech - Start the game with a Tech card. This card is considered completed and may be revealed when the Martian player is ready. Dots=command pts?

If I think of more ill let you know but hopefully this will be a good start for you. Let's us know how things work out.