Mod complete!
However did we manage before YouTube tutorials 
Hardest part was getting the bloody bottom cover off, DJI did not want us getting in to their controllers!
On the advice of @Ashmav I bought a ‘spudger’ tool kit on eBay for a couple of quid. It contains various nylon pry-tools, absolutely essential for performing this mod.
Few pics at random for you. First one here with the bottom cover removed and the top face-plate.
Don’t touch the screen!
You don’t want dust, fingerprints or dog hairs getting on it.
When removing the screen, DJI have kindly applied a spot of silicone glue to the bottom, to make it even harder to remove.
Because it wasn’t fragile enough already, they also stuck silicone on one of the bloody antenna connectors!
These ribbon cables are really fragile too 
Screen removed, antennas disconnected.
Antennas removed.
I struggled here to get the plastic clips to release, I actually destroyed both in the process. There’s no going back now!
Assembling the new quick-release connectors.
And installing and connecting them.
Bloody hell this part was fiddly. Big fingers and tiny delicate parts don’t mix. I had to be careful not to force the connectors back on. Alignment is critical.
Reassembly.
Done!
If you just want a quick flight you can use the 5dbi whips on their own. They’ll probably be a big improvement over stock, just on their own.
You don’t need to use the amplifier.
Full setup:
And with the CrystalSky in place:
First observations?
It’s bloody heavy with the CS attached!
The lanyard is essential.
My lanyard is clipped to the rear of the setup which means it naturally wants to tip forwards. Not sure if this will be an issue in flight or not. I might need to try and mount the lanyard more centrally.
Here’s how it connects to the car kit. I’m thinking you could use the car kit indoors too, just sucker the mount to a patio door window and fly from inside the house, HDMI cable to the TV… hmm…
That’s it, all done.
Mod took about an hour.
Just need it to stop raining now 