How to mask USB OTG as SD card I have a unique requirement wrt Youtube, MicroSD Card and USB OTG.

What I am trying to do:
I want to make use of Youtube offline feature where you can store a supported video offline (to view without any internet connection at a later date and time) in phone internal storage or attached MicroSD card.

The problem
The MicroSD slot in my phone is unavailable (because I am using the same for Dual SIM)

The non working solution 
I do have an OTG connector where I can add a MicroSD card to my phone, however the same is being detected as USB storage by the Android and hence by Youtube, and I am unable to store offline videos.

Help required 
I would like to know any app, hack, patch, custom ROM that will help me to use OTG as internal storage or mask the same as MicroSD card? 

Thank you all in advance for reading or replying to my question.
PS: I have "Redmi Note 3" as my phone running Android  5.1.1 and MIUI 8.0.5.0
I found a rather easy solution here, but it requires Android Marshmallow 6.0:

(My Device is a rooted Nexus 7 2012 with latest ASOP 7.1.2 installed, the OTG Device is a USB-Card-Reader with a Micro-SD-Card).
I'm note sure if you need root for these commands.

Connect your OTG-Device, then run the command in a Terminal-Emulator (like this one) directly on your device:

sm set-force-adoptable true


or use ADB from your pc (you'll need to install the Android Debug Bridge ADB first, see here):

adb shell sm set-force-adoptable true


After that, you should see a Notification, which ask if you want to use the storage "normally" or as adoptable storage (which would format the Usb-device). I chose the first one (without formatting), then the my OTG-Device was available like a Micro-SD-Card on my SGS5.
The OTG-Device will then automatically be mounted under /storage/0000-ffff (hex-code of your device).

Now i can choose my "new" SD-Card for Netflix Downloads. I assume Youtube offline downloads are supported now, too.

There is a Notification to "discard" your device, with that I even can disconnect the OTG-Device and/or restart my android, the next time I reconnected my OTG-Device I was able to use the Netflix Downloads again, without repeating the commands (sometimes I had to force-close Netflix first)!

With my OTG-Adaptor (Inateck OTG Hub &amp; SD Card Reader HB3001G) I even can use OTG and charge at the same time (connect the power source to the OTG Reader first, then to your Android Device, for some reason that dosen't work all thetime)!