Core Graphics: Drawing along a path with a normal gradient

There are a number of resources here and elsewhere on the web regarding how to draw with a gradient - fill or stroke.

However, AFAICT, none addresses the following requirement: how to draw a path with a normal gradient, whereby normal means orthogonal to the path. The net effect could be something like toothpaste or a tube when applied with a dark->light->dark linear gradient. Here is this idea in the case of a round rectangle:

round-rect tube http://muys.net/cadre_blanc.png

(this was hand drawn and the corners are not very good).

In the specific case of the round rect, I think I can achieve this effect with 4 linear gradients (the sides) and 4 radial gradients (the corners). But is there better?

Is there an easy solution for any path?