No, it is not possible.
miniOMNIAlog, to do correct measurements, needs to be powered or from the internal battery or from an external power supply (solar panel, electrical supply) to supply to the connected instruments the right tension and current.
Leaving connected miniOMNIAlog to the PC through USB cable, the instrument is powered directly to the PC. The USB port supplies a tension of 5Vdc and a maximum current of 500mA. These values guarantee the correct functioning of miniOMNIAlog for what concerns its management (configuration, web server surfing etc.) but they don’t guarantee the correct functioning in case of acquisitions.
Therefore, it is necessary to physically disconnect the PC from miniOMNIAlog during the acquisition cycles to do correct measurements.