I was puzzled by the hook as well, initially. I ended up screwing a SS coat hook underneath the rear deck. Can't remember what I screwed it into - might even have been the backside of the coaming there. That left me with the rope triangle. I took a line and put a knot in the middle to which I attached the becket of the lower block (in that setup, at the rear of the boom the main goes through 90 degrees down, 180 degrees up and attaches to a becket at the block where it made the 90-degree turn at the end of the boom, giving a 2:1).
I then fed the two ends of the rope (with the block in the middle) through the two stand-up blocks at either side of the transom and brought the two ends back together.
Now I had two ends and a hook. I solved this by "inventing" a knot that would tie the two ends together and also have a loop that would fit over the hook. The knot is a simple variation of a sheet bend. A sheet bend is used to tie two ropes together and has the same internal configuration as a bowline. (Grab one of the demos from the web if you don't know how to tie one). Anyway, in tying one, there's one rope that you bend into a U and the other end is used to complete the knot. For my variant you bend the second end into a U as well (doubling it) and then you tie a normal sheet bend with one side doubled. When you are done, there will be a short loop sticking out of the knot, that's the one I use to go over the hook. (Because of the way the knot works, it will hold if you pull on either end or the loop).
With a bit of fiddling, you can tie the knot so that you get the loop to be small (barely fits over the hook) and positioned where you want it.
I don't have a photo of it, but you get what I'm after if you double the red line in the picture below before tying, so you end up with a bit of loop sticking up. (The free end of the red line ends up on the right when you do it that way).

Phill gives a suggested height of the lower block from the transom when the hook is engaged. When you unhook, the block will no longer be centered, but pulled sideways, which reduces the amount of mainsheet you need for going downwind. If you forget to release, it seems to not make a huge difference, but it sure helps to have the knot hooked for upwind.