Is your USB socket active with the key out of the ignition? If the socket isn't active without the key in the Accessory or Run position, no switch is needed.
That said, a lot depends on how power hungry the WeBoost is, and whatever you have plugged into the USB outlet. If I'm not mistaken, most sockets can supply about 8-10 amps.
SMB-less as of 02/04/2012. Our savings account is richer, but our adventures are poorer.