It seems that you should be able to use the linux way by being in developer mode, opening crosh, and typing shell.
You then will have a bash shell, with the dd command.
Careful to use the correct device as target for dd.

I also see that the chromebook recovery utility can be used too - see here : https://www.reddit.com/r/chromeos/comments/7d02im/using_a_chromebook_to_install_an_iso_to_a_usb/

It really needs to be a permanent feature