I haven't seen any setting in the menus. There may be a setting in the unigine.xml file, but taking a quit look I didn't see one. Unless you have a video cable plugged into the integrated port, it can't be using the on-board. It has to be using the graphic system the monitor is connected to... the system Windows is using. Are your results poor? The on-board video would be practically a slide-show framerate compared to the GTX 570. If you have decent results, the GTX 570 is being used.
Can you provide a screenshot of the results window that gives you the false report?