Well, 'easy-peasy' wins the day.
I removed the throttle body adapter, and suspect corrosion weakened the bolt as that is where it broke.
Once removed, I tried my 1/16" left hand drill bit, and the bolt moved a tad -- so wasn't in there hard.
The bolt is apparently harder than the drill, or in any case, the drill was making little headway, though I kept at it.
By and bye, the bolt moved a little more. I then got out my needle nose pliers, and had the bolt another turn, and with that, was able to remove it with my fingers.
As mentioned elsewhere, I can't trust any of those bolts now, and have ordered a new set.
I don't know which ones I have, but I note on the Hermy's site they list "silver" and "stainless steel" as options, so I ordered the stainless set.
Thanks again to everyone who chimed in. I'm recording these inputs for future use. Thank you for passing it along.