rc = ioctl(fd, EMPEG_HIJACK_WAITMENU, NULL);

is the way to unbind from the display and menus. If you need to re-bind to the menus (so the app can be selected from the menu again) you need to do the above call followed by:

rc = ioctl(fd, EMPEG_HIJACK_WAITMENU, &menulabels);

But the latter is going to block your app until selected again. If you need stuff to happen in the background, you'll have to spawn a detached thread to do it.