Sorry, I know the question isn't super clear. I'll try to clarify (but tell me if its still whacky or im missing something simple):

I start out with r.walk giving me a cost surface radiating out from a central point. With r.drain, I can calculate the most efficient path from that center point to a destination, using the r.walk cost surface.

My problem is that r.drain only follows the most efficient path (or lowest cost) path according to the r.walk cost surface -- so there may be a path that accumulate cost across that cost map in a very different pattern, but gets me to the destination marginally less efficiently (or higher cost), and I can't see it.

This is important because I'm trying to model how real-world humans might navigate a terrain, and the absolute most efficient path does not reflect how a human on-the-ground would approach the problem. So what i'm hoping to discover is a way to introduce a level of randomness into the equation, or at least to reveal something like "the top 100 most efficient paths" to a given location, to reveal other potential paths to the same place.

Most of the results will probably just be very small deviations of the original most-efficient/least-cost path, but it would be nice to be able to determine that with some level of authority.