I would do what member “noromance” recommended. You could layer up the cardboard and cut to fit the plinth. Someone should design a platter puller, similar to what one would use to remove a steering wheel.
Help! Monolith turntable platter removal
I'm preparing to move house and wanted to pack up my Monolith turntable so I began what I thought was a simple process of disassembling the turntable. OK - it's not that simple. Can anyone guide me in removing the platter? I made the mistake of first disconnecting the drive belt, and now it's loose under the platter.
I emailed Monoprice, but don't know if their customer service is any good, so I thought I might get advice here.