Import Mac OS Volume (like we can do with Bootcamp)

Hi
Apologies if this has been asked before or the feature already exists.
I have created a dual boot machine so I can boot into Mojave normally or into High Sierra (by holding ALT during boot) so I can run older software that is not compatible with Mojave. Now what would be really handy would be if I could import that High Sierra Volume as a virtual machine (without having to create a new Virtual machine that takes up precious hard drive space). You can do this for Bootcamp where the same bootcamp partition is used both when you boot and when accessing it from Parallels. What I'd like to see is the ability for other Mac OS volumes to work in the same way.

This would allow us to boot into the same virtual machine depending on whether we want to harness the full machine's resources or just use Parallels to do some light work while still in the main host operating system.

If this feature already exists could someone tell me how to do it?

Thanks in advance.