I have just ordered a new back rest for my Humber console from Humber, I think they quoted £28 for the cushion assy, I guess they would also supply the stainless tube too, but Zodiac probably supply the correct bits separately anyway? It isn't on any of the pages or price lists but Humber seem happy to supply whatever bits required, you just need to ask.
Don't know how big yours are but I have just ordered a twin jockey (also from Humber) and I did wonder about doing that - but I think to cut it in half would make it a tight squeeze for people getting off and on, certainly on the one I am getting which is 31" long where it bolts to the deck - so probably a couple of inches shorter at cushion height.
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