Asus didn't add the ability to the webui, therefore I had to assume the hardware wasn't able to let you do so. You can always experiment with the wl command, but I can't give you any additional pointers since I don't have an RT-N16.
Asuswrt-Merlin: Customized firmware for Asus routers
Github: github.com/RMerl - Twitter: RMerlinDev
See the sticky post for more info.