[azimuth]

Each ID goes to its own footnote; each footnote returns to its own ID.
Repeated information for footnotes is set up as:
10. Collins, Language, 97.
11. Ibid., 101
12. Ibid., 101
13. Ibid., 112
14. Ibid., 112
15. Sanford, Genetic Entropy, 25-26.
16. Ibid., 53
17. Ibid., 53

Even if you had three ID's going to the same footnote....how will a footnote know which ID to go back to? It can't return to all three ID's -- only one of those ID's can it return to.

Kindle's asked for method is it, which means re-doing all 300+.

Someday in the future when pure CSS modal is recognized in all eReaders, then you would be able to have an alternate solution.