* USB /"Standalone installation" (where Opera doesn't touch the registry and doesn't create any shortcuts and doesn't make itself the default and uses a single profile folder) to current user's profile space and launch Opera.
"opera_installer.exe" /silent /installfolder "%userprofile%\My Program Files\Opera test install" /copyonly 1 /allusers 0 /singleprofile 1 /setdefaultbrowser 0 /startmenushortcut 0 /desktopshortcut 0 /quicklaunchshortcut 0 /launchopera 1
This one is just an example. You can do this right from the GUI and don't need the command line options.