Thanks your query and screenshots.
Apparently, the feature is not available. Well, Smart Markers feature is unique feature provided by Aspose.Cells API and you cannot always customize your desired changes as it has its own formatting/style. Anyways, could you provide us a simple template file (containing your smart markers) and paste your sample code (runnable) (or preferably a console demo application, you may zip it prior attaching here). Also, provide us your output Excel file and your desired Excel file (containing your desired formatted data having the bottom line to separate each group (you may update the output Excel file by Aspose.Cells and create your desired file in MS Excel manually). We do not promise that we can incorporate your desired change but we will surely look into it if we can support your needs in Smart Markers.
PS. Please do not use external database/data source, instead use dynamic DataSet/DataTable in your code, so we could execute your code with your underlying data.