const ProtractorConfigParser = require('protractor/built/configParser').ConfigParser;
const ProtractorRunner = require('protractor/built/runner').Runner;

const ptorConfig = new ProtractorConfigParser().config_;
ptorConfig.baseUrl = myExistingBaseUrl;
ptorConfig.seleniumWebDriver = myExistingWebDriver;
ptorConfig.noGlobals = true; // local preference

// looks similar to protractor/built/runner.js run()
const ptorRunner = new ProtractorRunner(ptorConfig);
ptorRunner.driverProvider_.setupEnv();
const browser = ptorRunner.createBrowser();
ptorRunner.setupGlobals_(browser); // now you can access protractor.$, etc.