Yeah I tried just now and it diesn't seem to be working (anymore?) could've sworn that worked.

You can still kexec the installiers directly, I followed the netboot.xyz scripts and got the links they use. Here's Debian as an example:

From the scripts: https://deb.debian.org/debian/dists/stable/main/installer-amd64/current/images/netboot/ looking at the boot config debian-installer/amd64/grub/grub.cfg

submenu '... KDE Plasma desktop boot menu ...' {
    set gfxpayload=keep
    menuentry '... Install' {
        set background_color=black
        linux    /debian-installer/amd64/linux desktop=kde vga=788
***
quiet
        initrd   /debian-installer/amd64/initrd.gz

so we need to download those two files and take the netboot.xyz cmdline arguments then

$ kexec --command-line="desktop=kde vga=788 mirror/suite=stable initrd=initrd.magic console=ttyS0,115200n8"  --initrd=initrd.gz -l linux´
$ systemctl kexec

and it boots.

also here's an example for the nixos netboot commands, more on that in the nixos manual:

$ kexec --load bzImage \
  --initrd=initrd.gz \
  --command-line "init=/nix/store/n37nmcvbrblk9ahfzj9nxy01axs7zsf6-nixos-system-nixos-kexec-25.11pre-git/init nohibernate loglevel=4 lsm=landlock,yama,bpf"
$ systemctl kexec

Edit:

No console access

If that means that you can only connect to SSH and have no VGA/video then this will be limited, you could setup an automated install but that requires a lot more knowledge than what your guide requires.