Do you have any similar pics showing the heater assembly?

Well... there already IS an aux water pump.
#5 in this picture below

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Just curious, why not arrange to run the FBH to heat the engine overnight.
The condition of the battery isn’t an issue, just install a permanent smart battery charger in the boot space connected to the car and connect mains power to the battery charger at night.
Forgive my simplistic thinking, no doubt someone will helpfully point out why this couldn’t be done.
I can’t see any reason why this wouldn’t work albeit the FBH would work more and might require servicing say annually.
Such an arrangement relies on more moving parts than an electric heater but as a side issue you would always have a fully charged battery, it also leaves the car as manufacturered.
Meantime I shall try and decipher the above diagrams.

In workshop manual is there a diagram showing the coolant flow direction in the system?
Pity you don’t have a Td6, l could show you where to install an aux heater on that.

Reading about the FBH on here, or on another RR forum, I found some did modify that system to make it heat the engine too.
It was just mentioned in a post, no description or anything, apart from changing or removing the change-over valves, as far as I remember.

This is the only schematic of the cooling system I could find.
As you can see, it shows the engine as one block, so it's not very useful to pick a place for a pre-heater.

Click image to enlarge

Well having tried to make out the coolant flow on the above diagrams l have to admit defeat, l just can’t figure it out.
The one thing l would definitely recommend is not to connect any auxiliary heater to the FBH pipe work. There are too many bits in the circuit to be able to guarantee they will be open to flow when required.
I still think the best place to connect a heater is into one of the coolant pipes to the cabin heater but this may not be practical due to the location of the pipes, the best option might be the pipe above the gearbox with two pipes run into the engine bay to connect to a heater.
Be interested if you proceed with this and what you do.
Just glad I’m now retired and don’t have to go to work on winter mornings with the prospect of having to start and then defrost a frozen car.

One would think / hope a location of a pre-heater is always part of the car and / or engine design.
Especially when we consider the RR a go-anywhere-anytime vehicle, right?
Of course the TDV8 users have the FBH and that's nice but LR designed and installed it in such a way only the interior is heated.
As if they don't care for the engine during low temp starts and rely on the proper 5W oil used.
(As a small side step, and certainly NOT trying to turn this into an oil debate!, I would like a 0W-30 in WSS-M2C948-B but so far this only comes in 5W-30)

The more I think about it, the more I like the pre-heater to be a clean, non-interfering-with-anything-bolt-on with a cable.
Much like the heater pads NobbyC posted.

I'll have till winter of 2022 to think of something.
And only if I can have a holiday north of the Arctic circle again

My hopes are now with the LR dealers in the south of Sweden.

The LR dealer in Goteborg gave me 2 websites to check for plug-in heaters.
The person I talked to said they installed aftermarket plug-in heaters 'all the time'.
One was the DEFA website, and it doesn't have anything for the 2012 4.4 TDV8.
The other was Calix, and it was promising as it has the 2010-onwards 4.4 TDV8 listed.
After looking at the installation pfd I found the engine bay position they showed was for a Freelander V6... so yeah...

IOW: nothing

Is the 4.4 TDV8 oil pan smooth enough to stick a heater pad to it?

 2012 4.4TDV8
2000 Honda S2000