The default Window list applet doesn't have this option, however there are alternatives. Icing Task Manager is the most popular. It replaces that applet and can also replace your launchers as applications can be pinned.
Right click your panel and "Add applets to the panel." Click "Download" at the top of the Applets window and you can download Icing Task Manager. After it has completed the download, you'll have to add it to your panel via the "Manage" tab. Select it from the list and click the "+" button at the bottom. Choose the "Window list" applet and click "-". Optionally, "Panel launchers" can be removed the same way.
This applet has many customization options to meet your liking.