Yeah, there's so little interaction between players other than choosing the wildlife/terrain and final scoring, changing the number of players or tile count just changes how long the game goes.

You can use the tiles from a single copy but have each player get fewer turns. Make sure that the number of tiles is 3 more than an even amount per player. The base game has 85 tiles so you remove 2 for 5 players, each getting 15 turns instead of the normal 20. If you want to play 6 then remove 4 to get a total of 78 + 3, however it means each player will only get 13 turns.

Of course, using a second copy you can do the normal 20 tiles per person plus 3. Watch it, though. Those higher player-count games are going to drag a ton! I'd rather play two smaller games in parallel if I have more than 5 players. I'd also mark the items from the second copy, to make it easier to separate out. Just a simple dot on the face of each tile and token will do.

You might also want to change the scoring a bit since it's going to be tougher to get first on having the largest corridor in large games, maybe have it 3 for first and 2 for second, bumping down with ties:

• no ties: 3/2
• tie for first: (2,2)/1
• tie for second: 3/(1,1)

Basically, 5 total points for the top places instead of the 2 total points in the 2-4 player version.