Classical mandolin players play individual strings & notes, but still use a pick (unlike classical guitarists).

For a sustained note, turn the tip of the pick almost-but-not-quite perpendicular to the strings and tremolo: (vibrate back and forth across the string pair).

Let me know if you've seen these before. If not, I can demonstrate somewhere that we'll be seeing each other, or I can poke around the web and seek some examples.