Store twice as many CDs in the same space.

Step 3 Take 2!

Pick the first (or last, it don't matter) 2 CDs,
Remove CDs and set aside (image 2),
Remove the trays. I used my thumbnail, although a thin, flat, non-sharp, non-pointy tool will do.
Examples: Butter knife, plastic spoon, credit card, guitar pick.
Note: If you choose to use your thumb(or finger)nail, remember that it/they may get chewed up in the process.
Insert your thumbnail/tool in between the tray and the U-card (printed layer in between tray and case bottom), and pry the tray out. (see cross-section diagram, image 4) Avoid inserting your thumbnail/tool in between the the U-card and the case bottom because doing so might damage the U-card.
Then slide your thumbnail/tool along the edge of the tray until one corner pops out, then slide it the other way to pop the other corner, or just pull it out at this point (image 5).
Repeat for the other CD case. (image 6)
Add the trays to your Stack-O-Trays (image 7).

When readying a case to be paired with an album you don't have yet, just swap the tray for a double tray. That's what I did with my Shine - The Hits CD, which will be paired with Thrive as soon as I get it.