How to apply effect to only one channel in sox?

I’m attempting to make a realtime voice changer to make me sound like a turian (from Mass Effect).

What I’d like to do, is take input from the mic, split it into two channels, lower the pitch on both but apply flanging to only one, and then mix them back together before outputting them to a pulseaudio sink.

Right now I’m having to just flange the whole thing, but it just doesn’t sound quite right.

Is there any way to do this with sox?