I needed to orginize my raspberry pi servers. They all use flirc cases as heatsink and a poe splitter from aliexpress since a poe hat doesnt fit inside the case.
Decided to stack the cases and it worked better then i thought. All LEDs are visible, SD card, USB and network ports accessible. Display and audio port are also usable, just a little harder to reach since they are now at the bottom of the case. 

All you need are:
2x Base

4x Extenders
8x m3 screws with length 20≥ mm

You can use a single base if you just want to organize your cases.