UniversalClassLoader::registerPrefix()

composer1.json

{
    "require": {
        "symfony/class-loader": "2.1.*"
    }
}

composer2.json

{
    "repositories": [
        {
            "type":"package",
            "package": {
                "name": "phanda/pathtranslator",
                "version": "dev-master",
                "dist": {
                    "url": "https://github.com/k-holy/Phanda_PathTranslator/zipball/master",
                    "type": "zip"
                },
                "source": {
                    "url": "https://github.com/k-holy/Phanda_PathTranslator.git",
                    "type": "git",
                    "reference": "master"
                }
            }
        }
    ],
    "require": {
        "symfony/class-loader": "2.1.*",
        "symfony/http-foundation": "2.1.*",
        "phanda/pathtranslator": "dev-master"
    }
}

loading.php

<?php
require_once realpath(__DIR__ . '/vendor/autoload.php');

use Symfony\Component\ClassLoader\UniversalClassLoader;

$loader = new UniversalClassLoader();
$loader->registerPrefix('Phanda_', realpath(__DIR__ . '/vendor/phanda/pathtranslator/src'));
$loader->register();

vendor.composer.autoload_namespaces.php

<?php

// autoload_namespace.php generated by Composer

$vendorDir = dirname(__DIR__);
$baseDir = dirname($vendorDir);

return array(
    'Symfony\\Component\\ClassLoader' => $vendorDir . '/symfony/class-loader/',
);

vendor.composer.installed.json

    {
        "name": "phanda/pathtranslator",
        "version": "dev-master",
        "version_normalized": "9999999-dev",
        "source": {
            "type": "git",
            "url": "https://github.com/k-holy/Phanda_PathTranslator.git",
            "reference": "master"
        },
        "dist": {
            "type": "zip",
            "url": "https://github.com/k-holy/Phanda_PathTranslator/zipball/master",
            "reference": null,
            "shasum": null
        },
        "type": "library",
        "installation-source": "source"
    }