If it's a particular cover page you want to insert (i.e. the user doesn't need to choose from the list) you could use a macro like:
Code:
Sub Demo()
Application.Templates("C:\Users\" & Environ("UserName") & _
"\AppData\Roaming\Microsoft\Document Building Blocks\1033\14\Built-In Building Blocks.dotx") _
.BuildingBlockEntries("Alphabet").Insert Where:=Selection.Range, RichText:=True
End Sub
Simply change "Alphabet" to whichever one you want to use.