Use EdmFunctionAttribute without exposing Entity Framework dependency/implementation details?

Question

Is there a good way to leverage EdmFunctionAttribute without introducing a dependency on The Entity Framework/System.Data.Entity.dll?

I thought I could have an interface with a method and a concrete implementation that implements the method using EdmFunctionAttribute to map it to a database function.

I have a context interface IMyContext defined in an assembly and an Entity Framework implementation MyContext in another assembly.

public interface IMyContext
{
    double SomeFunction(double first, double second);

    // other interface details here
}

public partial class MyContext : IMyContext
{
    [EdmFunction("MyNamespace", "MyDatabaseFunction")]
    public double SomeFunction(double first, double second)
    {
        throw new NotSupportedException("This method may only be called as part of a LINQ expression.");
    }

    // rest of interface implementation here
}

I use a factory (using StructureMap behind the scenes) to get a context instance as the interface type:

using (IMyContext context = ContextFactory.GetNewContext())
{
    var results = context.Table.Select(t => context.SomeFunction(t.Col1, t.Col2)).ToList();
}

This throws a NotSupportException saying that LINQ to Entities does not recognize the method 'Double SomeFunction(Double, Double)'.

If I cast the context to the concrete implementation

using (MyContext context = ContextFactory.GetNewContext() as MyContext)
{
    ...
}

then it works, but then I am required to specify the concrete implementation, which I do not want to do.

The function doesn't have to be a member of the context class, I just put it there for exploring.