Getting Babel 6 to work with IE8 (via. Gulp/Webpack) - internet-explorer-8

Question

I've got Babel 6 working nicely with Gulp and Webpack. I now need to polyfill it to get IE8 support.
I've installed the babel-polyfill, but can't get it working and the docs and Google haven't helped so far.
My Gulp task (inc. Webpack config):
gulp.task('webpack', function(callback) {
var webpackConfig = {
context: __dirname + '../../../js',
entry: {
homepage: [
'babel-polyfill',
'./public/homepage/homepage.js'
]
},
output: {
path: __dirname + '../../../dist/public/scripts/',
filename: '[name].bundle.js'
},
module: {
loaders: [
{
loader: 'babel-loader',
test: /\.js$/, // Only run .js files through Babel
include: /js/, // Only include the /js dir
query: {
//plugins: ['transform-runtime'], // Disabled pending fix to https://github.com/babel/babel/issues/2954
presets: ['es2015'],//, 'stage-0'
}
}
]
}
};
webpack(webpackConfig, function(err, stats) {
if (err) {
throw new gutil.PluginError('webpack', err);
}
gutil.log('[webpack]', stats.toString({
// output options
}));
callback();
});
});
From the docs (https://babeljs.io/docs/usage/polyfill/):
Usage in Node / Browserify / Webpack
To include the polyfill you need to require it at the top of the entry point to > your application.
require("babel-polyfill");
Usage in Browser
Available from the dist/polyfill.js file within a babel-polyfill npm release. This needs to be included before all your compiled Babel code. You can either prepend it to your compiled code or include it in a before it.
NOTE: Do not require this via browserify etc, use babel-polyfill.
I've tried simply adding the polyfill.js file to the top of the page, but IE8 still isn't happy with the compiled code's use of the default keyword.
I've also tried adding the polyfill to the webpack process, as per http://jamesknelson.com/using-es6-in-the-browser-with-babel-6-and-webpack/ and other suggestions from Google
What am I doing wrong?