Had a great time teaching my Boxes Chain this evening, and even though I really shouldn't have missed an opportunity for un-kitten-interrupted sleep (she's overnighting at the vet; recovering from her much-needed spaying), I was sure I could adjust the pendant for a rivoli.
Yes indeedy, and I barely had a false start.
Using a 14mm rivoli, the frame lies pretty flat, whereas without a rivoli, and only five units around, it's quite domed. This could definitely be scaled up for somewhat bigger rivolis (there ought to be a better plural; rivoli already sounds like a multiple), but that would require smaller beads (the biggest beads are 8mm in all the pendants I've made in this style). Smaller than 8mm and there may be too much air in the frame, too much space and not enough busy beading filling it up.
I'll have to try that another time when sleep isn't in quite such short supply. Like when I'm ten years younger again and twenty pounds lighter, in that dream.