Instructions for manually creating a macOS VM from an installer, without using scripts:

1. In terminal create an empty disk image: 

   hdiutil create -o "Installer.dmg" -size 15g -layout SPUD -fs "HFS+J"

2. Open the .dmg to mount it. It probably will mount as "untitled".
3. Follow the instructions at https://support.apple.com/en-us/HT201372 to create installer media, aiming it at /Volumes/untitiled.
4. Eject the new installer. Also use Disk Utility to eject the Shared Support image; there's a bug in macOS installers that leaves it mounted.
5. In Fusion, create a new VM.
6. At "Select the Installation Method", drag the .dmg file to "Install from disc or image".
7. Continue through the New VM dialogs as normal.

The VM will be set to boot from the installer disk image, attached to the virtual CD ROM drive. It doesn't matter where the installer is; there's no requirement that it be copied into the VM's folder.