UNTESTED.

This above setup is useful if you've got a fixed proxy url.
NOTE: adapted from x-ray request driver and added 1 line of code

Or use the below if you want to have a list of proxies under your own control

var Request = require('request')
var r = request.defaults({'proxy':'http://localproxy.com'})

let counter = 0;

//list with own proxies. 
//A simple way is to iterate through them in a circular fashion. This is called 'round-robin'
let proxies = [
	url1, 
	url2, 
	url3,
]

function makeDriver(opts) {
	if (typeof opts === "function") {
		var request = opts
	} else {
		var request = Request.defaults(opts)
	}	

	return function driver(context, callback) {
		var url = context.url

		request({
			url: url, 
			proxy: proxies[counter++ % proxies.length] // % is the modulo operation. Look it up if you're unsure how that works
		}, function(err, response, body) {
			return callback(err, body)
		})
	}
}

module.exports = makeDriver

You call the above driver as specified here