Check the drive number for your usb on windows using:
diskmgmt.msc
and looking for your USB drive.
Then, in a powershell admin terminal:
cd $env:ProgramFiles\Oracle\VirtualBox
# The number at the end of this command is the drive number. For this example, the drive number is '2'.
./VBoxManage.exe internalcommands createrawvmdk -filename "$env:USERPROFILE\.VirtualBox\usb-vm.vmdk" -rawdisk \\.\PhysicalDrive2
Then open VirtualBox and make a new Virtual Machine. When it asks if you want to create a hard disk, choose use existing hard disk
and select the file at $env:USERPROFILE\.VirtualBox\usb-vm.vmdk
. When you boot this vm, you will be running your live USB using VirtualBox.