Hi Sean,
I've just done one on this Sloper I'm sorting for a friend. As you say, not the easiest of tasks. Fortunately I have a lathe, so I turned a piece of tube and drilled it to be a good sliding fit on the post. I then clamped the kickstart arm in the vice with soft jaws to protect it. Assembled the swivel arm and washers with plenty lube and placed the offending circlip over the post and seated it with the short piece of tube by a deft clout with a hammer. If you don't have access to machine facilities, or know someone who has, perhaps you could hunt around for a piece of suitable tube.
Ian