Three options for adding extra players when you have proxy ships and planets but no destiny cards:
#1 — Destiny rules for the n+2nd player (after assigning the special destinies to player n+1):
- whenever a player draws his own color, he can optionally treat it as n+2's color
- whenever n+2 draws a wild, he can optionally treat it as his own color
It's not perfectly balanced, but then neither are the alien powers. It's close enough to make an n+2-player game playable.
#2 — A variation on #1. You can decide in advance that one of the players has to be Will. Draw 2n - 1 powers at random, add Will, and deal them out. If the player who is dealt Will chooses not to keep it, then any other player (starting to his left) can exchange the power they chose for Will. If nobody does so, then the player Will was dealt to must take it instead of his original choice. (I think somebody will want Will; it should be pretty competitive in a game with 7+ players.) When other players draw their own color, they may treat this as if they drew Will's color. Will may treat any destiny as his own color, so he can always encounter a foreign invader in his own system or reclaim an empty home planet.
#3 — Another option that's less attractive but scales up to 10 and preserves the special destinies:
Use a deck of playing cards. Number the players 1 through 10 (Ace equals 1, of course) and give each player his matching heart card to place near his planets. Use everyone's club, spade, and diamond cards to build the destiny deck, along with the Jack, Queen, and King of spades (Special Destinies) and the two Jokers (Wild Destinies). All the red cards (diamonds) are your hazard warnings.
This also gives you the option to fiddle with the DNA of the destiny deck, say by including more than three Special Destiny cards, or perhaps swapping out some spade royalty for diamond royalty so one or more of your Specials have hazard warnings.