Keeping root after OTA update?

Hi

I have Android 5.1.1 running with root on my Nexus 4 (using Nexus Root tool kit)

So there's a stock recovery installed.

There's Superuser installed.

There's an update waiting to be installed and I would like to keep the root or be able to root without losing data.

My phone has bootloader unlocked. And SU app installed.

Cheers

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