Watching Destin's video on whips...
https://www.youtube.com/watch?v=AnaASTBn_K4Because the supersonic portion of the motion is just at the very end of the entire wave of the whip motion, when the portion of the whip right before the cracker starts to pull the cracker in tension, this makes me think that you could just have a small bb on a string friction fit into place instead of the cracker. Like a tiny little press fit rod into the end of the whip. So the projectile would just be the cracker, but instead would be essentially like a tiny "hammer" (like olympic hammer throw).
The friction fit would likely be very finicky and need to be tuned well, because you'd want maximum energy transfer from the whip, so you wouldn't want it to slip out too early.
The other possibility would be just to make a tiny staff sling at the end of a whip. I think this would rarely work, and would require a very specific type of whip and whip motion.
The whip would need to resist twisting, so it would likely have to be a flat, and a long isosceles triangle with the mini-staff sling at the end. From the video, it seems that the motion of an unrolling-type whip movement would get it to pull the staff sling in the right way to get it to release. The bb pouch would have to be very cupped.