When you customize, click the Tools category on the left, scroll down to Macros on
the right and drag it to the toolbar.

Here's some code I posted almost exactly two years ago to this group:

===
Public WithEvents cbbButton As Office.CommandBarButton

Sub Dummy()
   MsgBox "Dummy"
End Sub

Private Sub cbbButton_Click(ByVal Ctrl As Office.CommandBarButton, _
CancelDefault As Boolean)
   Dummy
End Sub

Private Sub Document_BeforeClose(Cancel As Boolean)
   cbbButton.Delete
End Sub

Private Sub Document_Open()
   Dim cbBar As Office.CommandBar
   On Error Resume Next
   Set cbBar = Publisher.CommandBars("Macros")
   If Err.Number = 0 Then
       'everything is fine
   Else
       Set cbBar = Publisher.CommandBars.Add("Macros")
       Err.Clear
   End If
   Set cbbButton = cbBar.Controls(msoControlButton)
   If Err.Number = 0 Then
       'everything is fine
   Else
       Set cbbButton = cbBar.Controls.Add(msoControlButton)
   End If
   Err.Clear
   'you can insert some code to format the button here
End Sub
===

This creates a new button on a toolbar named "Macros", and calls the Dummy
subroutine.