The Austin Motor Co obviously thought about this problem early on. In the Austin Seven List of Spare parts Fifth Edition 353d under the tools section there is illustrated what they describe as 'Valve Cotter Tongs'. They look rather like sugar tongs but the ends are shaped to take the cotters. They cant have been much of a success as they dont appear in later Spare Parts Lists and for that matter, neither are they in earlier Lists. Later on you could buy patented Cotter Pliers made by I believe Scrivener, these are a bit of a fiddle and I still prefer the dab of grease method, which has always been satisfactory and quick for me.