Perhaps it would just be simpler to disable the original charging circuitry by removing D190 and D191.
This way, the Ricoh would be powered by the battery through R192, even while the system is running. And perhaps, replacing R192 with a wire would source less current from the lithium battery, extending its life.
Since my knowledge of #electronics is limited, to play it safe I might end up using the CR2032 adapter as designed. Suggestions welcome.