I believe that there is not a way to disable the IOS behavior of immediately sending an ARP request when you clear the table. And I do not understand why it would not be enough to see those ARP requests using ethereal, since they are the same requests that IOS would send if it need to find a device.
But having said that I believe there is a way to achieve basically what you want. If you shut down the LAN interface(s) the IOS will clear the ARP entries and will not send out the ARP requests. When you no shut the interface the router will not have the ARP entries and will learn the individual entries as it has need of them.
HTH
Rick
HTH
Rick