I think you can get that by setting `GRUB_TIMEOUT_STYLE=hidden` and `GRUB_TIMEOUT=0`. Then you can hold `Shift` to see the GRUB menu, otherwise it will boot the default option immediately.
Good tip. I've always felt like I'd like to be able to boot directly into the Second Option via a key, etc. like Shift + 2 etc
Make sure this works on your system before you really need it, as some keyboard/USB-controller combinations take a few seconds to wake up from whatever slumber they're in and start working. I ran into this several times.