It should connect automatically if you open a bookmark in the browser. From power on, you could try:

• Left side, top corner (I think that's the default location for the bookmark menu...)
• 1" from left, slightly above center: first bookmark.
• If you're in online mode, it should just connect.
  • If you're in offline mode, you'll shortly hear a notification beep; this signals the "Exit offline mode?"
  • D-pad center: selects OK
  • Wait ~10 seconds, while "Select connection" comes up and scans. Don't wait too long, though, or you may catch it in the middle of a rescan.
  • D-pad center: selects top entry, which will be a memorized connection if one is found.
• And you're done; should be accessible via SSH now.

Well, booting off an SD could work, if you used an image (e.g. Debian) preconfigured to automatically connect to your wifi, or to use a USB-serial adapter or similar...

The serial-console route is, in a way, perhaps the easiest to implement; it requires no screen input at all. You use flasher-3.0 to set the serial-console rd-flag over USB, and use a hacked-up USB-RS232 (w/o level conversion) cable. But that does involve soldering, and maybe jury-rigging a connector.