How to boot a VirtualBox VM from a USB block device

This procedure was tested using:

• A bootable (MultiBoot) UFD for the USB block device.
• VirtualBox 4.2.4r81684.
• Slackware64 14.0 host. 

These instructions below assume VirtualBox is managed via its GUI except where commands are given.

1. Plug in the USB block device and see which letter it gets by running the blkid command.
2. Assuming the the USB block device is /dev/sdc ...  create a VirtualBox raw device for /dev/sdc:
   

   VBoxManage internalcommands createrawvmdk -filename ~/VirtualBox/sdc.vmdk -rawdisk /dev/sdc

3. Create a new VM; choose "do not add a virtual hard drive".
4. Modify the new VM's storage, adding the .vmdk file created above.
5. Start the VM; it should boot from the USB block device.

TODO: does VirtualBox work with a symlink to the USB block device's device file?  If so, how about setting up a udev rule to create such a symlink so it does not matter if the USB block device is assigned sdc, sdd, sde ... .