You can do a lot of the pre-deployment configuration in the cloud but the device will need a way to download that configuration when it is hooked up.
I've done this with a few devices that were being sent to remote sites. One was an MX64 being sent to a satellite clinic with a static cable connection. I logged into the webUI on the device and configured the WAN information so that it would work once connected. Then I built the remainder of the config via the portal which the device pulled down once it was connected on-site.
Does that answer your question?