Você pode tirar proveito do comando 'npm cache', que baixa o pacote tarball e o descompacta no diretório npm cache.
A fonte pode então ser copiada.
Usando idéias obtidas em https://groups.google.com/forum/?fromgroups=#!topic/npm-/mwLuZZkHkfU, criei o seguinte script de nó. Sem garantias, YMMV, etc.
var fs = require('fs'),
path = require('path'),
exec = require('child_process').exec,
util = require('util');
var packageFileName = 'package.json';
var modulesDirName = 'node_modules';
var cacheDirectory = process.cwd();
var npmCacheAddMask = 'npm cache add %s@%s; echo %s';
var sourceDirMask = '%s/%s/%s/package';
var targetDirMask = '%s/node_modules/%s';
function deleteFolder(folder) {
if (fs.existsSync(folder)) {
var files = fs.readdirSync(folder);
files.forEach(function(file) {
file = folder + "/" + file;
if (fs.lstatSync(file).isDirectory()) {
deleteFolder(file);
} else {
fs.unlinkSync(file);
}
});
fs.rmdirSync(folder);
}
}
function downloadSource(folder) {
var packageFile = path.join(folder, packageFileName);
if (fs.existsSync(packageFile)) {
var data = fs.readFileSync(packageFile);
var package = JSON.parse(data);
function getVersion(data) {
var version = data.match(/-([^-]+)\.tgz/);
return version[1];
}
var callback = function(error, stdout, stderr) {
var dependency = stdout.trim();
var version = getVersion(stderr);
var sourceDir = util.format(sourceDirMask, cacheDirectory, dependency, version);
var targetDir = util.format(targetDirMask, folder, dependency);
var modulesDir = folder + '/' + modulesDirName;
if (!fs.existsSync(modulesDir)) {
fs.mkdirSync(modulesDir);
}
fs.renameSync(sourceDir, targetDir);
deleteFolder(cacheDirectory + '/' + dependency);
downloadSource(targetDir);
};
for (dependency in package.dependencies) {
var version = package.dependencies[dependency];
exec(util.format(npmCacheAddMask, dependency, version, dependency), callback);
}
}
}
if (!fs.existsSync(path.join(process.cwd(), packageFileName))) {
console.log(util.format("Unable to find file '%s'.", packageFileName));
process.exit();
}
deleteFolder(path.join(process.cwd(), modulesDirName));
process.env.npm_config_cache = cacheDirectory;
downloadSource(process.cwd());