This is basically a kernel module version of the python script xmm2usb found in James Wah's repository. Please be aware that this is a hacky approach that results the device to be reported by lcpci as:

02:00.0 Wireless controller [0d40]: Intel Corporation XMM7360 LTE Advanced Modem (rev ff) (prog-if ff)
	!!! Unknown header type 7f
	Kernel driver in use: xmm7360_usb

This is because the module disables the PCIe root port link, breaking all communication to the device, but the entry stays there because it has a driver in use. It should be pretty harmless though, and can be fixed by simply unloading the module with rmmod (which will also revert all changes though).

I have tested this to work with my Lenovo X1 Carbon (7th Gen) and do not guarantee it to work on any other laptop. Improvements are welcome though.

WARNING: There is a risk of bricking your laptop so you better know what you are doing from here onwards, remember you were warned.

Simply run the following:

make
sudo make install
sudo modprobe xmm7360_usb

Then after the modem boots in USB mode follow the instructions in the original repository to unlock the modem and set it to MBIM mode. Just to document it here as well, what worked for me was connecting to the serial and running:

at@nvm:fix_cat_fcclock.fcclock_mode?
at@nvm:fix_cat_fcclock.fcclock_mode=0
at@store_nvm(fix_cat_fcclock)
AT+GTUSBMODE?
AT+GTUSBMODE=7
AT+CFUN?
AT+CFUN=15

Everything simply worked on my machine from that onwards, and the automatically loaded module makes sure that the modem stays in USB mode even through reboots.