Software-only way to disconnect and reconnect a USB device?
if you felt bold, you could disable all of usb service and then reenable.  I believe that will do it.  will also kill keyboard etc.
kextunload IOUSBFamily.kext
kextload /System/Library/Extensions/IOUSBFamily.kext

it will take some more discovery, but i think this might be a good path.  let us know if you experiment
all usb extensions in 10.8 at least:
/System/Library/Extensions/IOUSBAttachedSCSI.kext
/System/Library/Extensions/IOUSBFamily.kext
/System/Library/Extensions/IOUSBMassStorageClass.kext