How do I set the default menu item in a ContextMenuStrip?

In my application I am using a popup menu item when right clicking an object. I dynamically build up this menu using code like this:

ContextMenuStrip menu = new ContextMenuStrip();
menu.Items.Add(new ToolStripMenuItem("Item1", aNiceImage, someFunction));
menu.Items.Add(new ToolStripMenuItem("Item2", alsoNiceImage, someOtherFunction));

Now I want to set one of these menu items in bold (as it is recommended by the Windows User Experience Guidelines) to indicate which action corresponds with double clicking the object.

How do I do this?