Azure Backup - Seeding

Hi all,

I have a client with a slow(ish) connection and a data cap, I would like to seed the data to Azure Backup. From what I can tell this can only be done by shipping a drive to a MS datacenter, but is it possible to create an offline backup to an external drive and import it from another location with a faster internet connection? For example: create offline backup to USB hard drive, take offsite (lets say my office), login to Azure Portal, import data from USB drive over faster internet connection.

Thoughts?