You have to find out where the USB input device resides - /dev/sda1, 2, 3 or else depending on your system/OS, and then "mount /dev/sda1 /mountPoint".
Again, this depends on the system in use, my usb drive is /dev/sda2 for example, plus I have automount - as soon as I plug the MP3 player or a USB dongle, it automounts it and KDE asks me what to do.