I have been scouring the web for the past week or so looking at righting pole ideas.
I think your ideas are great!
Obviously, the lighter the sailor, the longer the pole has to be. I don't agree that you have too many lines going. You actually have less lines running around than is the case with the triangle of lines in the set up for the commercially available righting pole. For the reasons you have outlined, the length of your pole requires the two lines. However, I agree that you should definitely use rope instead of cable.
I was wondering about two further possibilities. Rather than installing an attachment to clip the rope on to, could you not just run the rope around the trampoline support and then clip it onto a loop tied on the line? This would avoid drilling and screwing into the hobie.
The other possibility would be using some sort of rope hinge where the righting pole connects to the area just behind the upper dolphin striker. Perhaps running the last bit of rope that tensions the middle of the tramp through holes in the pole or better yet having it run through a loop of some sort that attaches topside of the pole. It is true that using the pole would cause the pole to push against the tramp rope. However, most of the force caused by hanging off the pole would be downward. There would be some horizontal/upward force against the tramp but not nearly as much as the downward force at the end of the pole.