Combining streams node

The return from this function needs to be a stream. In non-watch mode that's easy; just return rebundle, browserify stream is converted, blah blah, ok. In watch mode, however, rebundle is run on each update and creates a new stream every time. I need a way to consolidate all of those streams as they're created into a single endless stream that I can return and that can actually be consumed down the line. Playing with combined-stream, it seems like once data is read the stream ceases to be writable, so that's a no go. Any help would be appreciated!

var bundleify = function(watch) {

    var bundler = (watch?watchify:browserify)('main.js');

    var rebundle = function () {
        return bundler.bundle()
            .on('error', console.log)
            .pipe(source('main.js'))
            .pipe(rename('app.js'))
            .pipe(jsTasks()); // lazypipe with other tasks
    };

    // Regular browserify, just return the stream.
    if (!watch) {
        return rebundle();
    }

    // Watchify, rebundle on update.
    bundler.on('update', function() {
        rebundle();
    });

    // return ????
}