I cut out little rings of thin leather.
Before cutting, I affix double-sided carpet tape to the back of the leather. (I use some goat skin and it matches the camera leather pretty closely.) Then using a circle template I pen in the concentric circles, then cut them out.
Before affixing the leather protector, clean the eyepiece with alcohol and a cotton swab.
Mine have stayed on for over a year so far, and no sliding or scratches.
If you want a piece of leather, pm me.