You could create a Macro that typed the XAML into the XAML editor.
I tried creating a Macro the added directly to the design surface from the ToolBox but couldn't get it to work.
You can use a Macro similar to this and assign a Global hot key to run it.
Sub ButtonCreateMacro()
DTE.ActiveDocument.Selection.Text =
"<Button />"
End Sub
Cheers, Karl - Microsoft Product Team, Code Project MVP - http://karlshifflett.wordpress.com/