Can I install or use Portable VirtualBox manually?

Yes, you can and it's really easy. First download Portable VirtualBox.

Next, unpack it to the root of your USB key.

Then run Virtualize_This_Key.exe to directly launch your Linux in Windows or use VirtualBox.exe to display the full VirtualBox interface.

This will work with ANY LinuxLive USB key. No need to be created from LinuxLive USB Creator.

Obviously, no support will be given if you did not use LinuxLive USB Creator to create your USB key.