Two possible alternatives:
For Azure, if you want to remote-mount the disk, you probably want Azure File Storage, which is designed for that case, and exposes SMB-mountable volumes. It costs a bit more ($0.08/GB) than the basic blob storage though.
Rsync.net is a pretty well-regarded smallish company that does nothing but provide remote ZFS filesystems reachable over ssh. Could either sync to/from them with any tool that speaks SSH (rsync, duplicity, git-annex, etc.), or mount the volume with sshfs.
Note that this is for single-client use (e.g. backing up your personal machine) and from one location only. Your mileage might vary.