node.cloneNode() hardly seems like a hack. You can clone the node and append it to any desired parent element, and also manipulate it by manipulating individual properties, rather than having to e.g. run regular expressions on it, or add it in to the DOM, then manipulate it afterwords.
That said, you could also iterate over the attributes of the element to construct an HTML string representation of it. It seems likely this is how any outerHTML function would be implemented were jQuery to add one.