Hmmm... That may work. There are two issues. My prototype system (i.e. not the test rig I mentioned in the original post) runs on two PSUs (24 V for motors and 9V for everything else). When I hook up this system to a PC to upload firmware, I've noticed that it doesn't get enough current to run the USB host shield if the 9V supply isn't on. I'd have to check where the bottleneck is: is it the PC's inability to deliver enough current or the Arduino not delivering the current to the host shield? The other thing is that I'd rather have a through-hole or surface-mount component.