# Creating a 1G img file
dd if=/dev/zero of=disk.img bs=1k count=1048576
# Format it in ext2
sudo mkfs -t ext2 disk.img
# Mount it
mkdir disk && sudo mount -t ext2 -o loop disk.img disk/
#Extract your tar.gz in the mountpoint
sudo bsdtar -xpf yourfile.tar.gz -C disk/
# Umount your img file
umount disk

source : the internet...