There are some claims that suggest that umount will lead to a sync (at least in recent *NIXes) without having to do so manually. In any case, sync doesn't appear to lead to the device's LED turning off.
eject looked promising, so I gave it a try -- the results of sudo eject -v sdb were:
eject: device name is `sdb'
eject: expanded name is `/dev/sdb'
eject: `/dev/sdb' is not mounted
eject: `/dev/sdb' is not a mount point
eject: `/dev/sdb' is a multipartition device
eject: using device name `/dev/sdb' for ioctls
eject: trying to eject `/dev/sdb' using CD-ROM eject command
eject: CD-ROM eject command failed
eject: trying to eject `/dev/sdb' using SCSI commands
eject: SCSI eject failed
eject: trying to eject `/dev/sdb' using floppy eject command
eject: floppy eject command failed
eject: trying to eject `/dev/sdb' using tape offline command
eject: tape offline command failed
eject: unable to eject, last error: Invalid argument
FWIW, sdb does show up via dmesg and sudo blkid shows some /dev/sdb* lines. The syntax of the command looks right as one of the examples from the man page was: eject sda
I tried the sudo echo 1 thing, but no luck (Permission denied) -- may be I chose the wrong thing for what comes between devices/ and /remove...
Perhaps some day there'll be a straight-forward easy way to do this
Thanks all for your help.