I don't know of any way to fully maintain the Nook charge through USB while its operating. The standard USB micro plug cannot supply enough current even when connected to a USB charger 5v. That's why the B&N adapter has a special plug on it, to supply additional current.
Days of open internet are almost over as the biggies look for more revenue streaming from your wallet..Soon the internet will be a shell of its current self. With the government wanting their taxes and the big ISPs planning to charge extra for access to specific content (like facebook) and throttle your speed.