I've started working on an MVC 3 project that needs data from an enormous existing database.

My first idea was to go ahead and use EF 4.1 and create a bunch of POCO's to represent the tables I need, but I'm starting to think the mapping will get overly complicated as I only need some of the columns in some of the tables. (thanks to Steven for the clarification in the comments.

So I thought I'd give Massive ORM a try. I normally use a Unit of Work implementation so I can keep everything nicely decoupled and can use Dependency Injection. This is part of what I have for Massive:

public interface ISession
{
    DynamicModel CreateTable<T>() where T : DynamicModel, new();

    dynamic Single<T>(string where, params object[] args) 
        where T : DynamicModel, new();

    dynamic Single<T>(object key, string columns = "*") 
        where T : DynamicModel, new();

    // Some more methods supported by Massive here
}

And here's my implementation of the above interface:

public class MassiveSession : ISession
{
    public DynamicModel CreateTable<T>() where T : DynamicModel, new()
    {
        return new T();
    }

    public dynamic Single<T>(string where, params object[] args) 
        where T: DynamicModel, new()
    {
        var table = CreateTable<T>();
        return table.Single(where, args);
    }

    public dynamic Single<T>(object key, string columns = "*") 
        where T: DynamicModel, new()
    {
        var table = CreateTable<T>();
        return table.Single(key, columns);
    }
}

The problem comes with the First(), Last() and FindBy() methods. Massive is based around a dynamic object called DynamicModel and doesn't define any of the above method; it handles them through a TryInvokeMethod() implementation overriden from DynamicObject instead:

public override bool TryInvokeMember(InvokeMemberBinder binder, 
    object[] args, out object result) { }

I'm at a loss on how to "interface" those methods in my ISession. How could my ISession provide support for First(), Last() and FindBy()?

Put it another way, how can I use all of Massive's capabilities and still be able to decouple my classes from data access?