Rereading that minidisc.org page the JE510 is a machine that you cannot go
down that route.
Went down the lo-tech route. Dismantled a small part of the deck to get to
the eject/inject micro microswitch. Glued a bit of thread to the little
flipper and tied to a rubber band to hook over a suitable component.
Load as normal the donor MD full of silence, pull the thread, manually
rotate the eject gear to eject that MD, rotate the other way to take-in the
target disc. Go into Edit/name to force a TOC change and eject.
Recovered full recording without gaps, in stereo , and as a bonus undeleted
a bit of previous recording on the end