I've got to get myself a 3D printer one of these days, would have made this next bit so much easier.
So the handle has recesses sections with raised ribs so had to cut some pipe and slot it so it would fit inside the handle pipe.
Then I found some coated wire would do nicely for the raised sections but I would need to add some grooves to the inner pipe piece so it will sit better and give the glue something to hold on too, so I did this with the dremel and a file, luckily I had tape the right spacing width.
Then inserted in the handle and added the pieces of wire.
Next to slot the handle, this was just a test piece, should have 10 ridges.
Best I can do for now, as I said it's far from being 100% accurate.