Note to self: Use an external drive that has twice the disk space needed by the apps as a temporary mount point to restore to! Because it will need to download a copy of the whole backup, then unpack and finally bin the download. D'oh!
Step 1: Find a disk with sufficient space to restore to (apps space x 2)
Step 2: Mount the disk and symlink to the original location in the backup file
Step 3: Restore and then reset the storage location (or point it to where ever your new mount point is).
Got it all working now. Perhaps it's time to invest in a bigger SSD for my home server 🙂