Use physical disk on Win7

Run cmd as administrator. Run diskpart.

list disk
select disk 3
offline disk
attributes disk clear readonly
attributes disk

Exit diskpart.

Create vmdk file with:

"c:\Program Files\Oracle\VirtualBox\VBoxManage.exe" internalcommands createrawvmdk -filename d:\virtualbox\usb3disk0.vmdk -rawdisk \\.\PhysicalDrive3
RAW host disk access VMDK file d:\virtualbox\usb3disk0.vmdk created successfully.

Start Virtualbox and enter global settings. Change the path for VMs to D:\virtualbox. Close virtualbox and start it as administrator.

Choose you VM, click change, and add your vmdk file as harddisk. Start your VM and enjoy.