You would have to:
Creating your own alert template
If you want, you can create your own template, and then use the stsadm command to load that template. Pattern your template after one of the templates in Alerttemplates.xml.
A particular instance of a list can use a specific alert template by setting the SPList.AlertTemplate property with the desired template. Any new alert created for this list through the subnew.aspx or through the object model using SPAlerts.Add(SPList / SPItem, SPEventType, SPAletFrequency) will pick up the alert template defined for the list.
When that is done, add your new template to the list:
To assign a custom alert template to a specific list
Create a new custom template with a unique Name attribute in your working copy of AlertTemplates.xml (You can copy paste the entire section with Name SPAlertTemplateType.GenericList, change the name and modify the sections you want to). Modify the template as necessary. After restarting IIS, write object model code to set the list alert template.
SPAlertTemplateCollection ats = new SPAlertTemplateCollection((SPWebService)(WebApplication.Parent)); //give appropriate values for WebApplication
list.AlertTemplate = ats[“name from above”];
list.Update();
Reference: Customizing Alert Notifications and Alert Templates in Windows SharePoint Services 3.0