Hmmm....I just thought of a challenge that might be...interesting.

The Non-Melee Sora Challenge
In this challenge, Sora in no way harms another the enemy (unless it's a solo fight). Sora can heal his party members, but must rely entirely on them to defeat the enemies.

Going through the game like this could be tricky, given how lame your party members can be at times. This would be especially tricky on several boss fights. This wouldn't be much of a challenge for KH2, but might be for KH.

It might be lame, but it's all I could think of. And Vivi22 is right, the style of these games doesn't lend much room for a challenge of any kind.