I have upated bootmenu flashing script so it knows about newer firmware.
It also contains newer bootmenu code from SVN with menu timeout and ability to understand root device name like "ask:mmc2" to show menu everytimes but preselect mmc2 (and boot it after timeout).

You can still answer no on last question (flashing) and copy created initfs.bootmenu.jffs2 (and backup of original initfs) to PC and flash with usb flasher for extra safety. You need rsync installed on n770.

http://fanoush.webpark.cz/maemo/#initfs