require('lasso').configure({
        plugins: [
            {
                module: 'lasso-stylus',
                config: {
                    ... // See Configuration below
                }
            }
        ]
    });

require('lasso').configure({
        plugins: [
            {
                module: 'lasso-stylus',
                config: {
                    includes: [nodePath.join(__dirname, 'stylus/mixins/')],
                    use: function(stylus) {
                        stylus.define('add', function(a, b) {
                            a = parseFloat(a);
                            b = parseFloat(b);
                            return a+b;
                        });
                    },
                    define: {
                        sub: function(a, b) {
                            a = parseFloat(a);
                            b = parseFloat(b);
                            return a-b;
                        }
                    },
                    imports: [
                        nodePath.join(__dirname, 'stylus/variables.styl')
                    ]
                }
            }
        ]
    });