How to make a backup of app (game) data

Is there a way to take a backup (current stage, score, etc..) of a game app?
I am currently playing one game and want to to delete but would like to backup data so that when I come back, I don't have to start from scratch and just resume from the current stage. The game doesn't seem to offer any way to take a backup, though I can log in through Game Center and Facebook.
Only option I found was to backup and restore the iPhone. I took a back up, deleted the app and reinstalled just to check, but after logging to Game Center, it didn't resume, so had to restore the iphone.
Is there a way to backup just one app?