Step 6: Optional: Cushion your iPod
So first, cut your sponge to fit the dimensions of the extra space behind your ipod in the case with either a swiss army knife or an Exacto knife (scissors could probably even work). This is basically trial and error since I can't tell you how much room you'll have.
Next use strong double stick tape (I like carpeting tape) with your printed or drawn on paper to cover the sponge. I also used a black paint marker to cover the top and bottom edge which weren't covered by paper.
You can also try cutting a thin rectangular piece to pad the extra width room in the case. This helps to keep the case shut in addition to padding the case.