Here are some good methods of adding Mapped Content Controls:

• Custom Content Control Insert Dialog
• Insert Content Control Add-In by Graham Mayor, MVP
• Content Control Tools by Greg Maxey, MVP
• Repeating Data Using Document Properties Content Controls and Other Mapped Content Controls
• CC⁄V⁄BM & DP Tools Add-in

In my opinion, any of these is easier than deciphering the methods involving the XML controls on the Developer Tab. Perhaps I am simply lazy.