That would just be copying files from /home/ (vulnerable machine) to /home/ (appVM). Or from / (vulnerable machine) to / (templateVM). Cumbersome and if the way to root relies on i.e. Dirty COW (Dirty COW - Wikipedia) you are stuck with a 5.15.x-y.fc32-qubes.x86_64-kernel.
That’s just a quick and dirty writeup:
As mentioned in another thread I would like to provide a short how-to for resizing images of vulnerable VMs which then can be used in Qubes as HVMs. In your non-Qubes host system: download the current build of gparted-live (https://gparted.org/download.php) in virtualbox attach the gparted-live.iso as CD to your VM and boot into gparted-live on that VM resize the VM’s root partition to 6GB, 8GB or what seems feasable, most vulnerable machines should be smaller than 10GB shutdown VM and make i…

What you’re trying to do is literally one of the selling points of Qubes OS that doesn’t get talked about enough, and I wish it was publicised more…
HVMs are like VMs to other host-systems and for my part they deserve attention, too.
Before we further clutter the forumthread, we can continue to chit-chat via forum direct messaging.