Hi Nathan,
The addInfo is an object property and could not be added in the design page. So please use this property in the aspx.cs page. Please refer to the code example below.
Code example:
BasicShape node = new BasicShape();
node.Name = "node";
//define addInfo property
Dictionary<string, object> addInfo = new Dictionary<string, object>();
addInfo.Add("firstnode", "node");
node.AddInfo = addInfo;
Regards,
Shyam G