Determining which app is using serial port

[icefield]

I've spent a good while trying to figure out if there is a way to determine what applications has opened a handle to a serial port that is unavailable (owing to already being in use). CreateFile can tell if a COM port exists, even if in use, and I've looked at QueryDosDevice to see if there is more information there, but it seems like there nothing about the application using the port.

Any ideas?