Answer by karatedog for Linux - how to format multiple file systems within one file?

I would go with the tools I have in mind:

• create a new VM in Virtualbox with one disk, that would usually be /dev/sda
• boot into the VM with a GParted Live CD
• partition and format the disk in the VM to your needs (2 partitions, different file systems, etc.)
• then use dd to export /dev/sda to a file

With an educated guess it would take about 15 minutes.