Wifi Calling Extractable?

Hello,

I have posted this a week or so back but it was in my device specific forum and this I think is more of a general question, link to my original query is here.
Basically I want to unlock bootloader and root again as I have had my replacement back over a week now and I am clucking for root. I currently get Wifi calling on EE with their version of the firmware. I live in a pretty rural place and this is a REALLY handy feature. However, as I understand it this is baked into their version of the firmware so once I unlock the bootloader (G4 can't relock) I will be stuck without Wifi calling unless I flash back my first Nandroid, which will still be LP too (EE are verrrry slow at rolling out updates).
I wan't to know if there is any way (I am assuming almost definitely not) that there is an apk or setting I can extract and just flash in a modified ROM, stock or custom or if this feature will still be available somehow anyway? Before I got my replacement device I had the G4 with custom MM ROMs and wasn't aware that WiFi calling had been released for G4 yet (when I got my first G4 it was only available for iPhones and one of the Samsungs I believe but they have added a few more now) http://ee.co.uk/help/phones-and-device/getting-started-with-wifi-calling
It says there that it can only be used for devices bought direct off them so obviously must be in the firmware.
Waffling now

TLDR; As the title says, is there something can be extracted and injected into non EE firmware to allow Wifi calling, or does this need to be done at all?