Create a named disposableVM
Then use `qvm-open-in-vm` to open files in the new named qube.
Test this at the command line in your file management qube first.
You will also have to set policy in /etc/qubes-rpc/policy/qubes.OpeninVM
in dom0
Then set this ( qvm-open-in-vm <qube> ) as the default file handling
application - the right place to do this will depend on your DE -
perhaps ~/.local/share/applications/mimeapps.lst
If you want the disposableVM to close down when there are no open
windows, install the shutdown-idle service, and enable it in that qube.
Adjust the timer to whatever suits you: by default I think it is 5
minutes without an open window.
Having this work by double click will (probably) vary depending on what file
manager you are using.