It's quite strange that VMWare doesn't expose this feature in the UI directly, but fortunately enough it's pretty easy to do.
- Create a new custom virtual machine with macOS 10.14 as guest
- Quit VMWare after creating the virtual machine
- Change into the virtual machine folder
~/Virtual Machines/<name>.vmwarevm
- Connect your external harddrive with your SuperDuper! bootable backup
- Use
diskutil list
to figure out which device number your harddrive was assigned - Create a raw disk using the vmware-rawDiskCreator tool which is linked to the external harddrive: