The correct way to mount an ext4 sdcard on the stock 5.1 firmware+root?

So I have an unlockable bootloader on my Sony Z1C, so I can't (easily) run Cyanogen without doing some fun kernel repacking or finding the right rom. So far, I'm okay with the stock firmware. It does what I need it to do now that it's rooted.

The only issue, my SD card from my previous (now broken) phone is in ext4. Cyanogen automounts ext4 fine, but the stock firmware doesn't. I can use adb shell to mount it as root using the following:

Code:

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mount -t ext4 /dev/block/mmcblk1p1 /storage/sdcard1

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It mounts, but it's totally not viewable by any apps or in the Android storage menu. I found some threads that say to do the following:

Code:

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am broadcast -a android.intent.action.MEDIA_MOUNTED -d file:///sdcard

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But that doesn't cause my sdcard to show up.

All the instructions I've found are for older 4.x android versions and have tons of zip files and init scripts, vold files that don't exist on my rom, fstabs that don't exist on my rom, and garbage for all other versions of Android. What is the right way to mount my ext4 sdcard on the Stock+root Sony rom so it shows up correctly in Android OS for all my apps.

I really don't want to reformat it in vfat. It's a 128GB sdcard and is quite literally filled with all my music (well, A-W. I ran out of space. X-Z will have to wait..). I can mount it manually, so the kernel supports it. Is there something in build.prop I can enable so the stock auto-mounter will recognize ext4?