I just tossed that out as a "place holder example" -
But yeah, we should be looking for something different about executibles built for the old glibc and ones built for the new glibc.
If readelf does not give enough information, objdump will.
If no usable differences can be found in the elf header of old vs. new -
Then we will have to "mark" them ourselves (find an un-used bit/byte and set to a value that equals == Kindle Hack).
Sorry I can't be of more help, I am months behind in catching up with your work.