Hi
It is not possible. This USB port was suppose to be used as power supply to other devices. If you look at the devices documentation there is a warning saying, do not connect anything on this port or you may crash the AP.
"Usage of third-party USB modules with this Access Point is not supported. The behavior of such USB devices and the impact to the Access Point is not guaranteed. If Cisco determines that a fault or defect can be isolated due to the use of third-party USB modules installed by a customer or reseller, Cisco may withhold support under warranty or support program under contract. In the course of providing support for Cisco networking products, the end user may be required to install Cisco-supported USB modules in the event Cisco determines that removing third-party parts will assist Cisco in diagnosing the root cause for troubleshooting purposes. Cisco also reserves the right to charge the customer per then-current time and material rates for services provided to the customer when Cisco determines, after having provided such services, that the root cause of the defective product was caused by an unsupported device. "
And this:
"Cisco Aironet 2800 and 3800 Series APs have a USB port that can act as a source of power for some USB devices. The power can be up to 2.5W; if a USB device draws more than 2.5W of power, the USB port shuts down automatically. The port is enabled when the power draw is 2.5W and lower."
