I know this is a really old thread but I just had the same problem on the 12g escort my son uses and couldn't find an answer, then i figured out a way that doesn't involve loosing your fingers that works. So i thought i would post it her just in case someone else is searching for the same solution.
With the piston part removed clip the metal spring clip onto the recessed part of the piston.
using some grips squeeze the right angled tabs together as tight as you dare, then with some kite string or similar strong but fine thread wrap around the gap to hold the two ears closer together..
release the grips and if you have it bound tight enough the ears will be close enough they will easily slide in between the gap in the action bar.
Make sure the clip aligns with the recesses for the action bar and that the clip is toward the front so the action bar is located roughly in place.
Cut the string and the clip will pull out releasing the tension and hey presto the gun is ready for reassembly.
Took me a while to figure out but only to a few seconds to do once i had.
Cheers
ShootinFish
