EnumerationTypeConvention.cs

public class EnumerationTypeConvention : IPropertyConvention, IPropertyConventionAcceptance
{
    private static readonly Type OpenType = typeof(EnumerationType<>);

    public void Apply(IPropertyInstance instance)
    {
        var closedType = OpenType.MakeGenericType(instance.Property.PropertyType);

        instance.CustomType(closedType);
    }

    public void Accept(IAcceptanceCriteria<IPropertyInspector> criteria)
    {
        criteria.Expect(x => IsEnumerationType(x.Property.PropertyType));
    }

    private bool IsEnumerationType(Type type)
    {
        return GetTypeHierarchy(type)
            .Where(t => t.IsGenericType)
            .Select(t => t.GetGenericTypeDefinition())
            .Any(t => t == typeof(Enumeration<>));
    }

    private IEnumerable<Type> GetTypeHierarchy(Type type)
    {
        while (type != null)
        {
            yield return type;
            type = type.BaseType;
        }
    }
}