I've never done a powerstock before. I've seen them but this was just my go at it. It works, and it does help.
Materials needed:
1" PVC
1/2" PVC
1/2" PVC Endcap
Dremel w/ Cutting Wheel and a Grinding Drum
Expoy
Hot Glue
Spring (I'll say of your choice, but make sure it can nest in 1/2" PVC)
Thick Washer
Optional items:
Power Drill
1" Spade Bit
OK so here it goes,
Step 1: Cut the back end of that orange stock connecter off using the cutting wheel of the Dremel. Straightness is not a factor here the main objective is to have an opening for the new spring to connect with the plunger rod. For my Mod you will need something of the tube so do not cut at the base.

Step 2: Take either the Grinding Wheel attached to the Dremel or the Drill and Spade bit and grind out the 1" PVC pipe. What you are looking for here is a fit on one end that will slide over the remains of the Orange piece, the other end enough to hold the Endcap.
Step 2a: I say this is step 2a because the spring I used in this particular mod was premade for me from a friend. (whom if he wishes to come forward and say that is cool, but I will not say who it is without their blessing. Sorry) So this is my assumption on how to replicate this. It is fairly straight forward, but you take the washer, cut it down to fit in the 1" Pipe, or if it small enough no cutting required, but it needs to be big enough with no massive hole in the center to push back against the plunger rod. Hot glue the spring to it and let is set.
Step 3: The way I set my spring is, take a small piece of 1/2" PVC Just enough to either fit into the Endcap or a little over. Fill that up with hot glue and set the spring into the glue. This way the spring won't come loose.

And is should look something like this.
Step 4: Assembly. Mix up some epxoy. I used Loctite (I think) plastic epxoy, only one I had, but it works. Put the epxoy on the orange tube from the Stock Cap. and slide the pipe on.

Then add some epoxy to the other end and fit the Endcap spring combo. Let it sent and then reattach to the blaster. The Pipe I had left enough room for me to be able to actually screw the Stock Cap back on so it is fully removable.
Final Product:

Firing Demo
[I will post a firing demo later as this was actually a commission and my friend is getting this later today]
This is not ranged tested, however I was noticing an increase in velocity in shots when I was testing it after assembly. I would say this probably improved the range by 10 feet, but testing in my garage at my Garage Door 20 feet from where I was. Stock shots were hitting the door and bouncing back 5 or so feet off the door. With the Powerstock attachment, then were bouncing back to me or within 5 feet of me, and some were almost straight shots back.
Questions, Comments, Constructive Criticism.