There's a number of dongle-security products out there, such as the "
Dongle Lockbox". My inclination is to believe that these products will only deter casual, opportunistic dongle theft, and won't be much protection against someone who already knows that you have a dongle, and comes equipped with the minor tools necessary to liberate it from your machine.
I suppose a more secure way to do it would be to install an internal USB PCIe card in your machine (assuming you have a tower), and install the USB dongle internally.
I've always wondered how software vendors secured their dongles in environments such as a tradeshow like NAB. Seems like the only way to secure them would be to physically secure the entire computer itself.