Get Navigation Properties of given EntityType

I am using VS2010, EF4.0. Need function like the following.

private string[] GetNaviProps(Type entityType)//eg typeof(Employee)
{
    NorthwindEntities en = new NorthwindEntities();
    //here I return all Properties only for example
    return entityType.GetProperties().Select(p=>p.Name).ToArray();
    //should return Orders,Territories...
}

I have checked this, but IObjectContextAdapter seems something in EF6.0 and .net4.5. I tried to replace it like

var workspace = en.MetadataWorkspace;

So it can compile, but exception throw at the 3nd line then.
Any help?