however bad these examples are, they show the basic way to pipe stuff into node-tar

gistfile1.js

function createEntry(data, path, root) {
	var entry = new stream.Readable();
	var allpushed = false;
	entry._read = function(s) {
		if (allpushed) {
			this.push(null);
		} else {
			this.push(data);
			allpushed = true;
		}
	};
	entry.props = {
		type: "File",
		mode: 0644,
		mtime: Date.now() / 1000,
		size: data.length
	};
	entry.path = Path.join(root, path);
	entry.root = root;
	return entry;
}
var root = "mydir/"
var tarStream = tar.Pack({ noProprietary: true });
var sourceStream = new stream.PassThrough();
sourceStream.props = {type: 'Directory'};
sourceStream.path = root;
sourceStream.pipe(tarStream, {end: false});
tarStream.add(createEntry("file content here", "test.txt", root));