Again, thinking out of the box.
You say the line will not run through the pulleys.
Have tried using Dynema, or even Dacron cord.
Both smooth and used in sailing. Very flexible, and Dyneema is smaller diameter (for a given strength) and slippery.
Both come in white, but dacron stains easily with boot polish, I imagine wood dye as well. I have not tried to dye Dynemma.
As for the elastic being too strong.
What if only a short section below deck was elasticated. This would reduce the pull.
Or you could try what the sailing boys do to maintain tension on winch drums. Where a ring on a piece of elastic is used to pull on the line and maintain tension.