How to mount an ext4 formatted external sdcard in stock Android 4.4.4?

I upgraded from the Note 1 with cyanogenmod 11 to the Note 4 (910C) with stock android (rooted). I want to use the ext4 formatted external sdcard, but Samsung does not added ext4 support for the extSdCard (WHY???????????), so it is not being recognized at boottime. Anyway, I managed to mount it, but I am only able to use it as root. Yes, the ooold permission problem.

I used this script for this:

REALMNT=/mnt/media_rw/extSdCard 
mount -t ext4 -o rw,noatime /dev/block/mmcblk1p1 "$REALMNT"
sdcard "$REALMNT" /storage/extSdCard 1023 1023 &

This script does mount the card, but with the wrong permissions. I also changed the permissions in /system/etc/permissions/platform.xml, no luck.

Some permissions I get after mounting the sdcard manually:

# ls -la /storage (notice 1015 instead of 1028)
  ....
  drwxrwxr-x 13 0 1015 4096 Jan 29 02:52 extSdCard

# ls -la /mnt/media_rw
drwx------ 9 1023 1028 0 Jan 29 03:30 .
drwxrwxr-x 7 0 1000 0 Jan 29 03:30 ..
drwx------ 2 1023 1023 0 Jan 29 03:30 UsbDriveA
drwx------ 2 1023 1023 0 Jan 29 03:30 UsbDriveB
drwx------ 2 1023 1023 0 Jan 29 03:30 UsbDriveC
drwx------ 2 1023 1023 0 Jan 29 03:30 UsbDriveD
drwx------ 2 1023 1023 0 Jan 29 03:30 UsbDriveE
drwx------ 2 1023 1023 0 Jan 29 03:30 UsbDriveF
drwxrwxrwx 13 1023 1023 4096 Jan 29 02:52 extSdCard

Clues?

Thanks!