Marshmallow and setting the external SD card as internal storage

Hi can anybody advise on if it is possible and if so how to set the external sd as internal under the stock firmware?
I know it's possible on the AOSP/CM based ROMS but for the life of me I can't find how to do it in stock.

I've tried searching on XDA but haven't had any success in finding any references.

This is on an 910F

Thanks for reading

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