What I have come up with is a piece of
1 4 foot Stainless brake line.
1 Lenght of Vinyl clad Staimless cable.
2 Swedge ferrules.
2 Eye bolts. Or Hook Bolts
2 Stainless Nuts.
2 Flat Washers
Basically you would Cut the brake line to the size of your hard plastic cover, then thread the wire through the Brake line, then make a small loop on the end and swedge it tight.
Then feed that loop through the top, and hook it on the Hook bolt, repeat for the other side....
The lenghts are what I don't know..... but it will be easy to hook or unhook, totaly be replaceable at minimum cost, and with the stainless steel wont rust, and you can then really smash it in with out having to worry about breaking the cable.
You make as small of an eye with the cablew on one end and swedge it that way it will feed through the top hole I was thinking of using 1/8 galvanized vinyl clad cable about 79 cents a foot you need roughly 14 feet so that is about 10 bucks, using the hook bolts will allow you to hold the eye that you made and you then can tighten it with the nut.
Eye bolts, nuts and ferrules are probably 5 bucks, the brake line is about 6 bucks so for about 25 dollars you have a better quality of a cable, that will be easy to replace over the years,

What we need is the lenght of the cable from the top of the bolt to the top of the other bolt, then the Outside diameter of the hard plastic part, then the total lenght of the bolt.
If some one has one laying around then measure it for us and we all have a better than the 40 dollar TMI cable and less than the 149 dollar Genuine VW cable...
So feel free to use or abuse.