sd card - Invoke /system/bin/sdcard manually via terminal

I am trying to mount an EXT4 formatted SD card under Cyanogenmod 13.1 (Android 6.0.1).

So far, I have setup scripts to mount the card at /mnt/ext_sdcard during boot. My current understanding is that the "sdcard" service must then be invoked to create a FUSE mount pointing to the real mount point which will eventually lead the media scanner to the newly mounted disk.

Following some older older documentation and forum threads lead me to this command in terminal:

service sdcard /system/bin/sdcard /mnt/ext_sdcard /mnt/test 1023 1023
    class late_start

When I run the command (as root of course), it fails with an exit status of 1 and no output/error messages.

My question: Am I doing something wrong, or is this command deprecated in 6.0.1 (the documents/forum thread seemed to relate to KitKat)? What is the correct syntax/arguments for using this command?