I really liked the model by @Gypo_282797 and asked him for model files, but i never heard back - so I created my own version.

Rather than to use magnets and scratch the metal tray, I suggest using double sided tape.

This version was made to suit the aftermarket parts I have:

NEOUZA flat base tamper: https://www.amazon.com.au/dp/B08BFRKJ32

NEOUZA magnetic dosing funnel ring: https://www.amazon.com.au/dp/B0B1W97XZ2

NEOUZA bottomless portafilter: https://www.amazon.com.au/dp/B087WM4T7J