I've been doing some testing and research on how to make the engine start easier when cold and i think i've got a solution - however it involves reflashing the ecu (any decent ecu mapping place will be able to do it - or £15 cable from ebay).
Whole thing is based on warming up glow plugs with higher current for longer.
So far i've only tested this on my own car 2.4 210BHP, with glow plugs like in this photo https://jacekowski.org/cold_start/DSC02351.JPG
I'm using NGK glow plugs that i've changed about 6 months ago for a brand new set.
This video shows how easy it is to start https://jacekowski.org/cold_start/VI...120_070221.mp4
It was actually Wayne from Autolusso that gave me the idea to look for it somewhere else, initially i was just looking into extending pre-glow times but it didn't really do a lot, and then when i was talking to Wayne he mentioned that glow plugs run on PWM in this car.
Details below are ecu software version specific - addresses might and will be different if you have different software.
My software version is 506095 - also identified by F38JTDA6 at 0x1C001A (latest available for my car).
The changes i've made are:
Doubled glow plug PWM values at 0x1CF64C (originally 45%), 0x1CF64E (originally 35%), 0x1CF650 (originally 25%) - smaller changes did not really do a lot.
extended glow times in 10x7 map at 0x1CF2B4
I've been running with the changes for past month with no negative effects.
It will probably reduce glow plug life but i don't know by how much and it's just a matter of waiting for first one to fail.