How do I model bind in asp.net mvc 3 to an already created instance?

[birdfun]

I'm attempting to get model binding to work with an existing object. I'm pretty new to MVC so forgive me if the approach is bad.We have a large patient object. The process is, the patient is first loaded, stored in the session, then edited across multiple pages. We don't want to create a new instance every time model binding occurs because only a subset of properties have been edited. The patient lives in a temporary state until a hard save occurs and then the patient is saved to the database.I'm trying to take advantage of model binding in asp.net mvc 3, but realized that a new instance is created each time it occurs.I'm not certain how to accomplish this task.