pitch shifter?
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EQ+Compression on clean?
Pitchblack - Fulltone Octafuzz - Hardwire OD - Blakemore Effects Deus Ex Machina - MXR Micro Chorus - Diamond Memory Lane Jr - EHX SMMH - Neunaber Wet
He could be doing something to the strings you're not seeing. Banjo sounds like a guitar with the strings slightly obstructed in a way that they don't sustain(probably be opposite of compresser then?).

Can't think of how you'd get it short of using MIDI pickups.
That banjo part isn't actually being played, if you watch closely.

The guitarist just launched a sample off of his Digitech JamMan Looper - basically a sound clip of the actual banjo. That's really about the closest you might be able to get - banjos have that resonating head, remember that.

You COULD try maybe for a sitar type sound, that's about the closest you might be able to get... For sitar type sounds, I just set a delay pedal to a ridiculously short delay - maybe about 10-20 ms, mess around with the feedback knobs til you get it close. It's not even a perfect sitar sound, but its just something i like to do to mess around sometimes.

Or, the Line 6 Variax guitars (basically a modeling guitar) has a banjo model built, and the variax models sound pretty decent - maybe you could look into that.