Not sure capture one has much control over this, that's a camera design issue. Most cameras I've encountered switch over entirely from card when connected to a computer.
In the Canon SDK its actually a driver manageable setting if the camera should save to card aswell as through USB connection. Hence why several other solutions provide this feature but not C1.
And yes, i have cursed quite a few times over the lack of this feature in C1 when the USB buffer is overloaded on MacOSX (with the latest patches) and C1 locks up and the shots taken but not sent through usb are lost.