Using blend is the way to go. Blends over complex curves aren't easy to control though—you end up with something like this:
An easier way is to create your blend on a straight path and create an art brush form your blend. Controlling blends with varying strokes also isn't easy so I would suggest using 2 separate blends.
Create your first blend:
Duplicate the blend, decrease the stroke width and rotate 180°:
You can edit the paths to create the angled joins. Just select the overlapping end point (if they aren't already in the same position—move them so that they are) and move them to get your desired result:
The S shape is significantly longer than the blend we've just created so simply move the paths on one end across—make sure your blends were created with a specified distance (not steps) otherwise you will have to increase the number of steps:
Create an art brush from your blends. You can do this by selecting the blends and dragging them to the brushes palette and selecting Art Brush from the New Brush dialog.
Get the center line of your S shape. I did this by quickly drawing a path over an S character, but you may be able to use a negative Offset Path to get a more accurate path.
If your shape has a consistent width or stroke weight using a negative Offset Path will get you the center line easily enough.
(Object → Path → Offset Path...)
In the case of an uneven stroke weight you can repeat the offset path command a number of times to build a guide to draw your center line.
An easier way is to again use a Blend. Remove the closing segments of the path at both ends and ungroup or release compound path so that you have to distinct paths and create a blend with 1 step. This should give you the center line (You may need to create the blend in segments for more complicated shapes if the blend fails).
You can find more techniques for finding the center line in this post: Technique for finding the centerline of a curved object?
Apply your art brush to the path:
This isn't perfect but you can easily go back and adjust your blends or the S shape to get a better result.