It only now occurs to me that somebody should have purchased thousands of rubber ducks[1], then traversed the 7th arc[2], tossing one* overboard every mile or so.
Here's a pdf of a poster where someone did basically that, using computer simulations of course. Their figure 5 shows debris zones [edit: actually garbage patches] that are pretty close to Reunion
Update: To do this correctly, you'd need winds, and the approx windage of the object. Coast Guard search and rescue simulations take this into account. Wind can push objects on top of the ocean currents.
That's a good point about the windage. I'm skeptical that you can really conclude much about the original impact site from a single piece of debris anyway. On the other hand just being able to narrow the origin down to even one half of the arc might be beneficial at this point.
[1] https://en.wikipedia.org/wiki/Friendly_Floatees
[2] https://en.wikipedia.org/wiki/Analysis_of_Malaysia_Airlines_...
* Appropriately labeled with GPS coordinates of release, of course.