I doubt you'd be able to pull a flat polyester webbing strap through the hole of a pool noodle. Plus, pool noodle floats will compress down pretty quickly. The structure of the cells of that expanded polyethylene is not all that robust. I used them on my lifelines, as I often sit on the coaming top and lean back against the lifelines. I expected them to give out pretty quickly, and they did. Also, they started to disintegrate after about a month and a half due to the UV, which I also expected. I've heard of folks putting suntan lotion on them to reduce this. I just went ahead and bought some of the less expensive Taylor Made cushions.
There is nicer neoprene pipe insulation out there. It's pre-cut down the length, with pressure adhesive on the edges of the cut. Again, I doubt it would fit on the strap, but it might be slightly more compression resistant than the polyethylene of the pool noodle.
It's all academic, though, because Piotr just needs new covers on the existing padding.
I think you'll find you need to get someone to sew them up for you, perhaps with velcro closure. Most padded hiking straps I'm seeing from googling look to have padding and covers sewn onto the strap. If you're at all handy with a sewing machine, it would not be difficult to make with some Sunbrella and velcro. My worry for you is that a round sleeve around the padded strap may rotate and not feel too secure.
Another place you could ask around would be the Gear Anarchy or Dinghy Anarchy forums over at Sailing Anarchy,
http://forums.sailinganarchy.com. Just be aware, Sailing Anarchy takes no prisoners, and gives no quarter, so get your thick skin on before you head over…
Brian