You can do this using reflection
public static Report GetReport(ReportTypes reportType)
{
Type t = Reports[reportType];
MethodInfo method = typeof(ReportFactory)
.GetMethods(BindingFlags.Static | BindingFlags.NonPublic)
.First(m => m.Name == "Create");
MethodInfo genericMethod = method.MakeGenericMethod(t);
return (Report)genericMethod.Invoke(null, null);
}