You can have renderings assigned on standard values of templates, each new item would then have your PageTeaser rendering.
If you wanted to automate this process have a look at the <mvc.getXmlBasedLayoutDefinition>
pipeline, we are injected common renderings by extending this pipeline.
Updated
I've found some code samples and blog posts that should help point you in the right direction for manipulating the layout details.
public void AddSublayoutToItem(string itemId, string sublayoutId)
{
using (new Sitecore.SecurityModel.SecurityDisabler())
{
if (Sitecore.Data.ID.IsID(itemId) && Sitecore.Data.ID.IsID(sublayoutId))
{
//Get the master database and get the item on which you want to add sublayout
Database masterDatabase = Database.GetDatabase("master");
Item item = masterDatabase.GetItem(Sitecore.Data.ID.Parse(itemId));
// Or you can also get Sitecore Item from Context Database as per your requirement
// Item item = Sitecore.Context.Database.GetItem(Sitecore.Data.ID.Parse(itemId));
if (item != null)
{
// Get the layout definitions and the device definition
LayoutField layoutField = new LayoutField(item.Fields[Sitecore.FieldIDs.LayoutField]);
LayoutDefinition layoutDefinition = LayoutDefinition.Parse(layoutField.Value);
DeviceDefinition deviceDefinition = layoutDefinition.GetDevice(Sitecore.Context.Device.ID.ToString());
//Create a RenderingDefinition and add the reference of sublayout or rendering
RenderingDefinition renderingDefinition = new RenderingDefinition();
renderingDefinition.ItemID = sublayoutId;
//Set placeholder where the rendering should be displayed
renderingDefinition.Placeholder = "content";
// Set the datasource of sublayout, if any
renderingDefinition.Datasource = "{24240FF2-B4AA-4EB2-B0A4-63E027934C38}";
// you can also set datasource of sublayout using Sitecore Path
// renderingDefinition.Datasource = "/sitecore/content/Home/Books";
//Add the RenderingReference to the DeviceDefinition
deviceDefinition.AddRendering(renderingDefinition);
// Save the layout changes
item.Editing.BeginEdit();
layoutField.Value = layoutDefinition.ToXml(); ;
item.Editing.EndEdit();
}
}
}
}
Taken from here - http://www.bugdebugzone.com/2014/06/how-to-add-sublayout-to-sitecore-item.html
Also a couple of other blogs on the topic