I've done this mod on a few applications with success. Just did it again on a set of ProLine Powerstrokes for my Slash 4x4 because the ball kept popping out and it was driving me crazy!!!
Pretty simple to do, just a couple of things you might want to think about if something like this would work for you.
I chose a set of HPI HB 6.8mm ball-ends for these shocks (part #'s HBC8100 and HBC8089). These are quite a bit beefier than the stock ProLine ends and would actually carry a slightly larger diameter shaft. In other words the Powerstroke shaft will bite into it but won't get a tight purchase. A little trick here is to apply some CA glue (or even hot glue if you're quick) to the threads. This will help fill the space. Here in this picture you can see the size difference between the stock ProLine and the HB above it:
It's worthy of noting a couple things here: the HB ball-end is a few mm longer than the stocker, so we know some pre-load adjustments will have to be made. Also, the outer diameter of the rod-end shaft is much larger than the stocker and the spring cup will not accept it. Time to let Mr. Dremel off the leash and whittle it down a little Just trim it down enough so that the spring cup won't be forced around it:
And all mounted back up: