That is the video to his design.
I'm a tinkerer, so, in no offense to Mr. Kay, I wanted to make this fit my needs.
What I did:
I attached another pen tube to the top of the canister to allow me to look where I'm shooting, thus allowing me to aim.
I took the second pen tube, filled the smaller end with some silicon, feel free to use epoxy I didn't have any on my bench.
Then, I drilled a small, like 1/8 in, hole in the side of the 2nd pen tube.
Next I smeared, rather sloppily, silicon where the pen tube would be.
Finally I zip tied the whole thing together, forcing it to keep solid.