During World Tour mode you can unlock the rewards for Gold (hard) and Silver (medium) while still playing the game on Easy difficulty. Just enter the event or tournament and select Gold (hard) difficulty. Once done, before your first match, exit World Tour back out to the main menu and press (square) to bring up the options menu. Change the game difficulty back to easy, then go back to World Tour and the match/tournament you selected. It will still say Hard but when you play the match it will be on easy difficulty and if you win you will still unlock the rewards for beating it on Hard.