That's exactly right, Shoe. The glass was sprinkled on and then just patted down, but that wasn't sufficient.
So I used a thin smooth piece of plastic (a cutout from the 3ml lamination, actually) to run over the rest of the stone and then over the glass. That action just barely dragged some thin concrete over the glass. It also had the effect of smoothening out the stone's surface so that any sharp glass edges were laid on their side.
When we were done, you could hardly see the glass at all because the concrete had been spread out. This morning when I brushed it off, that extremely thin layer washed right off with no trouble but the glass is held fast.
I think after it cures for about a month, it'll be so firmly embedded that it'll never come out.
