How to set value for property of an anonymous object?

this is my code for example:

var output = new
{
    NetSessionId = string.Empty
};

foreach (var property in output.GetType().GetProperties())
{
    property.SetValue(output, "Test", null);
}

It occurs an exception: "Property set method not found". I want to know how to create an anonymous type with properties which can be set.

Thanks.