This is more of a fun glitch really
You will need: The special 2d costume from acing last level in lbp 1
Hook hat

Step 1: Put on the special costume (its located in torso i think)
Step 2: Put on hook hat (you should not look like the special sackboy any more)
Step 3: Take off the hook hat now by entering the power up menu and selecting the hook hat again
Now you should be a special sackboy inside a normal sackboy

Sorry I just had to share this because I think I'm the first to find this out

That's a pretty funny glitch.