Thanks. Yes, the goal of the step-down on the cable end is to improve the strain relief. I tried earlier rigid solutions, but found that they soon frayed below the fix. My attempts with tape started out well, but eventually the tape would slip and the heat shrink would slide down. The silicone tubing has more "grab".

I think you are visualizing it correctly. Let's see if I can replicate it with ASCII art (not to scale):

  ------------------------------ 
      ==========================******************
    =========================*********************  
  ++++++++++++++++++++++++++++++*********O********
    =========================*********************
      ==========================******************
  ------------------------------  ****************
                                  ****************

  - layer of heat shrink -------   Rigid Connector
     = outer layer of silicone =******************
   = inner layer of silicone =********************
  + Thin frayed Apple cable ++++***color O led ***
   = inner layer of silicone =********************
     = outer layer of silicone =******************
  - layer of heat shrink -------  ****************
                                  ****************
 

It comes out looking quite nice. The rigidity of the tubing plus shrink wrap isn't a problem if you plug in so that the rigid part is along the side of the laptop. It actually provides a fairly nice handle for unplugging, since you can get good leverage anywhere along the shrink wrapped portion.