How To Make NHibernate Serialize A Given Property To A Binary Field

I have a simple ASP.NET MVC web application that uses NHibernate with FluentNHibernate's auto mapping feature for its data access. I have encountered a scenario in which I would like NHibernate to persist some classes as binary data.

public class User
{
// This field will be persisted
public virtual byte[] PortraitData { get; set; }
// This method will get me what I'm actually interested in
public virtual Image GetPortrait()
{
return SerializationHelper.Deserialize<Image>(PortraitData);
}
}

(I leave the implementation of the SerializationHelper class to the reader's imagination. It doesn't do anything complicated, just serializes and deserializes data into byte arrays and back.)