Tom Quigley just published an excellent viewlet on the brand new Ensemble 10.3. His demo highlights how straight forward it is to inject content into any web application.
Here is a brief summary of Ensemble:
Ensemble is a reverse proxy through which end users view Web applications. For example, a customer might control access to and collect analytics on their wiki by proxying it through Ensemble. They might also use Ensemble to inject existing portlets or widgets into new Web applications.