I think this is best achieved using the built-in ClientScript capabilities of ASP.NET. Instead of tricking the column of the grid in order to store the additional information, maybe you can use some of the methods provided by Page.ClientScript.RegisterXXX methods - for example RegisterArrayDeclaration, to send different values for the given key (could be the field Key of the column).
Later, you can use javascript to access the information from the array and associate a given key with its respective values.