Generic and non-generic interfaces

I come across a lot of situations where I have declared a generic interface and later I needed a non-generic version of this interface, or at least non-generic version of some of the methods or properties on that interface. I would usually declare a new non-generic interface and have it inherit the generic interface. The problem I am running into in shows in the example below:

public abstract class FormatBase { }

public interface IBook<F> where F : FormatBase
{
    F GetFormat();
}

public interface IBook
{
    object GetFormat();
}

public abstract class BookBase : IBook<FormatBase>, IBook
{
    public abstract FormatBase GetFormat();

    object IBook.GetFormat()
    {
        return GetFormat();
    }
}

Since the only way to declare the IBook (non-generic) interface is explicitly, how do you guys go about making it abstract?