All you have to do is make sandbag the only item, and put items on high.
Then you make a "CD Factory" in the custom stage builder. There are a variety of ways to make them. By doing this, i got 8 CDs in about 5 minutes :O
Here is what one looks like:
YouTube - CD Factory (Smash Brothers X / Super Smash Bros. Brawl)

(i made a better version IMO )

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