Yep. It's a tricky one this. Have tried it some time ago and this is what I have found:

Use a USB stick in the same usb port. Windows will pick it up and give it a drive letter.
You can then eject the drive letter.

BUT

Plug a light in the same usb port, and windows does not give a drive letter as it's not a drive.
...it does not work. There must be another way to do it...