How to release control of USB devices back to MAC OS X

I am having issue whereby when I go from my virtual Windows window back to a Mac OS X window, my USB devices are not available to me. I have to go and uncheck my USB external drive and iPhone when I go back to MAC OS x when back in a USB window. Is there a way to have them released automatically? Problem is I have a autmated back tool running and it needs to access the USB drive. However if Parallels does not release control from virtual windows machine, then my automated backup fails. How do you get around these issues. When I try to sync iPhone it can;t because the iPhone is not available. Once I uncheck it in the USB menu, it works again.

Thanks and I look forward to your reply.

...B

 

Device can be removed from VM using command line tool. So, you could detach it from VM at the beginning of backup and attach it back after.

This is possible using 'prlctl' utility
prlctl set VM_NAME --device-connect ''DEVICE_ID
for example
prlctl set Vista --device-connect ''1d100000|1310|0001|full|--|2E59400D0B00''
prlctl set Vista --device-disconnect ''1d100000|1310|0001|full|PR|2E59400D0B00''

The list could be create using
prlsrvctl info