You can't simultanouesly share a USB device using the same interface. You might want to consider a USB-to-Ethernet connector which "might" allow the device to be networkable. Then, connect the device to the Ethernet hub/switch and install the corresponding software on the devices.
But in the meantime, the only solution you have is your current setup, which I also have in sharing my HP Deskjet 895Cxi printer with a PC and a Mac.