DetailsView - No Insert Button when DefaultMode is Edit

[cheshire2k]

I'm using a Master/DetailsView model for my site.

<aspetailsView
runat="server"
ID="dvw_Customers"
AutoGenerateRows="false"
GridLines="None"
DataSourceID="sql_dvw_Customers"
AutoGenerateInsertButton="true"
AutoGenerateEditButton="true"
DefaultMode="Edit">

When I click on an item in the Gridview, the DetailsView shows an "Update" button and a "Cancel" button. There is no "Insert" button. How do I get this thing into insert mode?