I bought a cheap bimini off ebay, ripped off it's bottom mounting hardware, filled the bottom of the pipe with a wooden dowel for rigidity, drilled a hole through it. I used a Hollaender Adjustable Elbow Tee Body 17M
to connect it to my frame. I used spare snap pins
to connect the bimini to the Hollaender fitting.
I can easily slide the fitting along my outer frame rail (but only on one side of the oar towers). And, it uses the same parts/tools as needed for other parts of the frame, which keeps the repair kit small.
Worked well for me and was all said and done for about $120. Well worth it for a windy trip on San Juan.