I have a Cyberpower UPS connected to my system using USB (for power management). Sometimes I want to have this device accessible from within Windows 7, which is virtualized in VirtualBox. VirtualBox correctly detects that the USB device is currently is use by the host OS, so it won't connect. My workaround is to create a device filter in VirtualBox, then unplug and reconnect the USB cable while VirtualBox is running. I would like to know how to make OS X stop the device without physically unplugging the cable.
I'm running OS 10.9 Mavericks.
ioreg
command should show you when the device is connected, but you might need to get VirtualBox to just grab the device all the time rather than on connection for your needs.