Note! This is for the wireless version of the Connexion mouse with the square base.
This is a mashup of a similar base for the wired mouse. I added the base from a storage case for the wireless mouse.
I did this on Tinkercad. The source is public so you can tweak it if you want.
If I were going to print it again I would make the mouse holder thinner so the USB clearance wasn't so tight.
I printed with Cura tree supports for the USB cable holes. It would probably print fine without them.