I am not sure what you mean by "too tall." Are the stamps physically too giant to fit into a CD case, or are they too thick to fit?
If they are too thick, make sure you have removed the black insert that allows the CD to clip in. If they are too giant to fit inside a CD case, I have read about folks using DVD cases. I've seen some in the electronics section by Memorex, but I am not sure if the insert that the DVD clips into comes out on those, or if they are molded right into the case. I have found some double-CD cases at London Drugs that work well because they snap entirely closed, with no gap like regular CD cases with the insert removed have.
Sorry I could not be more help, but there are lots of other UM fans on SCS who are super helpful.