your N7 must be rooted to use Stickmount.
For unrooted N7 you can use Nexus Media Importer available on Play Google store
Nexus Media Importer allows you to import and stream music, video, photos and documents from a USB flash drive or SD card connected to your Nexus 7 & 10 ...
Update: NMI does work with 4.2.2, but people have had issues. Try opening NMI, then connecting the USB device. If that does not work, try uninstalling and reinstalling.