I need a longer seatpost than what is commonly available (or available at all?) to ride the ubiquitous MTBs, so I weld two seatposts together. That's all fine and dandy but the leverage of having that seat being 12" away (from the frame to the clamp) is pretty bad from a structural standpoint. Sure enough, over a couple year's use my long seatposts begin to bend back. Luckily it has been just the posts and not the frames!
Anyhoo, I've just made the answer for this:
and it seems to work.
It is a light gauge tube, flattened and drilled both ends with the upper end under the seat clamp nut and the other attached to a clamp around the frame tube made of duct strapping, isolated with bicycle inner tube rubber mainly to keep from scratching that immaculate paint.
This being my winterbike, the salt was awful tough on it even though it was a record-breaking mild winter. I wire brushed the corrosion off the post, greased it, and installed that nifty bicycle inner tube sleeve to keep the grease on the tube and off me.