Hi Pietro -
Using Sites IN a MVC framework is very difficult, because the entire context of WebCenter Sites is burned into the COM.FutureTense.Servlet.SContentServer servlet. You can't really work around that with any degree of reliability. Unfortunately, that means that dropping Sites into a pre-existing third party MVC framework doesn't really work.
There are a lot of good reasons for that, not the least of which is the two-tiered pagelet-level caching system that makes Sites so very fast at delivery... not that it's any consolation.
To deal with this some former colleagues of mine and I built the GST Site Foundation ("GSF") framework, which provides a Spring-like MVC container WITHIN sites, instead of the other way around. If you're familiar with Spring, you'll see patterns similar with the GSF. My current team and I have blogged about this extensively:
The full stream is here: GSF | Function1
But ultimately, the special sauce is the following: in Sites, create an XML element that contains nothing but a <FTCS> tag, a <CALLJAVA> tag, and a closing </FTCS> tag. Your CALLJAVA will then call a class that implements the Seed or Seed2 interface, and from in there you have access to the (properly managed) ICS object where you can do all of your magic. You can then build a lightweight controller here to handle any action you can dream up:
Let me know if I can help!