I think it comes down to HOW you play as opposed to WHAT you play. Granted, flatwound strings with the tone rolled off and possibly a foam mute under the bridge will get you in the neighborhood. But I think someone who has spent some time playing upright is going to know what that attack and decay of the instrument sounds like. Pulling a string and hearing the note bloom or what note durations in a walking line should sound like come from hands on experience. Really good electric players can at least mimic that sound, but I don't think there is any gear combination that will give you an instant upright sound. Look at Will Lee. He has gone so far as to actually play upright and recently I saw him playing a Line 6 VariAx, because he knows he isn't going to get an upright tone out of an electric.