Wire detent mod pictures start in Post #26 on page three of this thread. Automag style ball detent in cocker barrels?
That was 5 years back. I've done 3 barrels for other folks and all have reported that they worked as well for them as for myself. For my markers I've used this trick with three autocockers and a good half dozen cocker body or Nelson style pump markers with great results.
The only drawback is that the stub has to have enough "meat" to allow turning the groove. So far I've found that it works with autococker threading and SL68II slip fits as well as the Line SI barrel. Most others are too thin to allow this mod to be done. One which is too thin is the Phantom threaded barrels. But the solution for that style is the detent rings they come with.