Here's an adapter case for the Ploopy Nano Trackball and the BDN9 Macro Pad. It combines the two peripherals by replacing the bottom housing/plate of each device, though they'll still need to be plugged in with separate cables.
I remapped my BDN9 in QMK to act as the mouse buttons and scroll wheel(s) to have very versatile and ergonomic thumb trackball (depending on hand size and finger length your mileage may vary.) Keep in mind that the Ploopy Nano still requires a micro-usb cable while the BDN9 requires a separate usb-c cable to actually work.
The print in the images was printed off of a Kingroon KP3S Pro with a standard 0.4mm nozzle and 0.2mm layer height, and should be able to be printed without supports. I recommend you stick some rubber feet to the bottom to prevent slipping.