Forgive my if I might a take a different approach. I was looking at 4mm D12 line (which is pitless) and will run very smoothly through the blocks. Just where you want to grab it during sailing I would like to put in a conventional but souple 4 mm line as a filler. When you compress D12 line lengthwise its diameter increases to such an extent that you can peel it over the conventinal line easily. It also provides a smooth transition point where the thin line thickens. Byu pulling the D12 line it wil tighten itself over the filler.
Has anyone tried this before?