This house (vintage 1960) was inspected successfully about ten years
ago when we bought the house, but I'm not aware of any external GFCI
feeding these switches There is one on an outlet in the other bathroom
(not hooked to this bathroom), and the bathroom we're talking about
has only nongrounded outlets that feed from the wall lamp over the
sink. (No, not that smart either, especially because they are switched
with the light, but at least not reachable from the shower. No
nightlights going on those outlets!)

I guess I have to believe that the inspectors didn't consider it a
code violation. Perhaps they would have if it were an outlet? Probably
right that these switches simply aren't considered shock hazards. I
find that a bit surprising. The fact that there aren't GFCI swtches
handily available would be consistent with that.

Back to the original question. Hacked or not hacked, how would I put
one in? Surely there is a dual toggle switch that has a GFCI built in?
Or are you saying that I need to put in a new box next to the switch
box, put a GFCI outlet there, and feed the switches from that circuit?
Seems unnecessarily hard.