you can modify the out of the box mxd's installed with ArcGIS server (on the server they are located in C:\Program Files\ArcGIS\Server\Templates\ExportWebMapTemplates) instead of publishing you own. Just add a text element (insert>text) then open its properties and click on the "Size and Poistion" tab and give it an Element Name (ex: infoDetails) this will be referenced in your template parameters.In the below example I'm referencing the customTextElement infoDetails and passing in a string (details) that I generated. This also shows you how to access multiple customTextElements.template.layoutOptions = { titleText: "My Print page", customTextElements: [{ infoHeader: headers }, { infoDetail: details }], }hope this helps.