Print using Add-in Only (Excel 2010, VBA)

In fact, why not do this:

Public Sub Workbook_BeforePrint(Cancel As Boolean)
    PrintDoc
    Cancel = True
End Sub

Public Sub PrintDoc()
    Name = UCase(Application.UserName)
    ctrlNbr = "12345"
    Call PrintDocX(Name, ctrlNbr)
End Sub

Then you effectively cancel normal printing, and do the add-in printing instead, without the necessity for an error message.