Specify Packages Manually in Composer

composer.json

{
    "repositories": [
        {
            "type": "package",
            "package": {
                "name"    : "twitter/bootstrap",
                "version" : "2.1.0",
                "source"  : {
                    "url"       : "https://github.com/twitter/bootstrap.git",
                    "type"      : "git",
                    "reference" : "v2.1.0"
                }
            }
        }
    ],
    "require": {
        "php"                   : ">=5.3.3",
        "silex/silex"           : "1.0.*",
        "twig/twig"             : "1.*",
        "kriswallsmith/assetic" : "1.0.*",
        "fate/silex-extensions" : "dev-master",
        "shuber/curl"           : "1.0.*",
        "twitter/bootstrap"     : "2.1.0"
    },
    "minimum-stability": "dev"
}