If you REALLY want to get spiffy put a connector on the back of the Filco. It's not that hard but will introduce another point of failure (like Panda-R's Ducky).
It's another point of failure, but at the same time it seems like the ability to release under high strain can be a huge positive for durability of the keyboard. So long as the mounting of the connector is strong enough (get something
like this that's screw mounted, instead of something just pcb mounted), the most likely scenario is simply that the cable will release, rather than ending up with strain on connections internal to the keyboard, isn't it? If something is going to be damaged, it's probably going to be the connector's contacts in some way, which just means replacing the connector if it does happen.
If something is causing cable failure other than strain (such as small chewing animals >.> ) then having the cable be easily replaceable is *definitely* the best, in my opinion. I would have a lot less cables with bits wrapped in electrical tape after being respliced if I could just plug in a new one =P
Really I think the base reason for wanting a more durable cable is ultimately going to determine a lot about what the best solution would be, but I think a connector and being able to replace the cables seems like one that would cover most cases very very well.
As to the monoprice cable's awg for the actual wires in it, I suppose you could roll your own usb cable if wire awg were a concern. I wonder if STP would work, I don't know what the usb spec calls for...