Its pretty easy to do yourself. Have done 2. No issues.
If again, would use a plate as a washer and try to find a nut to fit the flush cup threads.
Adhere (gorilla glue) some solid material behind where you are placing, drill and thread.
I did tap mine and glued cups in.
Did one I doent glue cups in (was a work in progress when I sold it).
Easy and best option if you arent into tinkering is to send to Jducos.