On my quest to make the hornet a worthwhile primary, I figured out what I consider to be its greatest flaw. Whenever you need to re-pump, you need to move the slide forward and back, or "re-trigger," as I call it. Once you re-trigger, however, you can't fire the barrel(s) you still have loaded. This just kills usability in the field, by making strategic reloading more akin to a retreat.
From there, it was my goal to make it so you could repump whenever, and still be ready to fire the other barrels. If you know anything about back pressure guns, you'll know this is harder than it sounds. Once you pull the trigger on a hornet or blastfire or the like, a pathway is opened from the back of the tank to the open air. This means whenever you try to pump, the tank can't hold any pressure.
My solution is perfect - it closes off the connection to the open air whenever you repump, but only to the fired tanks. Concurrently, it opens a channel directly to the pump to put air into the tanks. Whenever you're fully pumped and ready, you can re-trigger and push a button, and the system returns to a fully primed state.
Did I mention it's extremely simple to do?
Materials:
Five (5) 1/8" Tubing Tees (Mcmaster part: 9675T33 [pack of five])
Five (5) 1/8" Shuttle Valves (Mcmaster part: 6667T14)
Extra 1/8" tubing
It's pretty straight forward. Splice 5 Tees anywhere between the pump and the trigger mechanism (white tube that holds orange piece, splits to all 6 tanks), run each of those lines into one input of the shuttle valves, run the output of the shuttle valves into the tanks, and run thes line that used to run into the tanks into the other input on the valves.
I figured a diagram would be much simpler to understand than a picture of my finished jumble of tubes:

Recap for legibility:
5 Shuttle valve outputs into first 5 tanks
5 Tees between pump and trigger mechanism
5 lines that used to run into the tanks into an input on the respective shuttle valve
5 lines from the Tees into the shuttle valves' other input, in any order.
From there, you just need to hook a blast button into the line somewhere between the pump and trigger mechanism. This can be simply made from one of the existing buttons, or several other ways.
Done!
Protips:
The outputs on the shuttle valves are the leg on the T shape.
You can rearrange the firing order of the tanks to whatever you like!
To use:
If the gun is already "re-triggered," pump to full, and press your blast button. Ready!
If the gun is partially fired, pump to full, re-trigger, and press your blast button. Ready!
If the gun has been fully fired, re-trigger.
Final product:
Here's how mine turned out-


Notice how I managed to conserve space on the inside with the tubing. It allows me to keep the gun looking as if it were bone stock. I do hope the judges can find it in themselves to look past the pump replacement. That's neither part of this mod nor writeup, and is the only thing that makes it look non-stock externally.

Keep in mind that mine is arranged to fit into the shell, and be ready for the "Hornette" minimization mod.
Closing:
I feel this mod adds near-infinite functionality to the Hornet, allowing you to not need a sidearm even. It's easy to replicate, and pretty clever, if I do say so myself

Hope this gets some new ideas turning. The uses for "shuttle valves" are very wide ranging. I find this mod to be only the first step.