Fabian -
I believe your question was concerning the use of a "Sneaky Pete" and has anyone ever used one.
Well, I will be happy to answer your question.
I have used a Sneaky Pete to replace the top rope seal on my 261. They are made by the Lisle Corporation and are nothing more than a corkscrew type of tool with a wire and ring attached to the corkscrew. It is actually pretty easy to do, but you need to take your time and do it right. The most important thing is to properly prepare for this challange.
To specifically answer your question, "Yes", they work well and you can do the job without pulling the engine.
Take your time, and good luck!
Joe