I've seen where the fibers come separate, and you mix them into the concrete yourself.
I would be curious to know how you would direct the pipe down there. Maybe an anchor or two with a rope, and an eye loop on the pipe to guide it? If the pipe is lighter than water, it will be hard to keep it where it needs to be with a 20ft length.
It seems easy until you start thinking about the difficulties of aligning the pipe to the hole and keeping it there while you are working. Maybe craft something that has a rod/steak on the end that you pound into the bottom to have it stay put while you work, with a 45 degree fitting to angle material where you need it.
Another option would be a bucket with a trap-door bottom that you can open with a second rope to dump the contents once it is guided over the hole. It would need to be a lot heavier than water to work.