The Loog Piano has an optional magnetic stand that attaches to magnets on the top of the piano. 
These Gridfinity Baseplates can snap onto those magnets. For added stability, I designed a custom bracket based on the Screw-Together baseplates, which can be fastened to the piano with some reusable double-sided tape.

The magnets I used for the bottom are 7x3, with 2 on each side. Unfortunately they don't have a lot of holding strength. I might do some more experimentation with bigger square magnets that better match the alignment on the piano.