Как насчет просто:
var dataStructure = new[] {
new { col1 = "something", col2 = "something else", col3 = 12, col4 = true },
new { col1 = "ha", col2 = "ha ha", col3 = 356, col4 = false },
new { col1 = "grrr", col2 = "grr grr", col3 = 213, col4 = true }
};