You might try to mechanically create a "shutter cut" by masking off a portion of lens at each emitter. The traditional "donut" is a piece of black-wrap or Cinafoil (black extra heavy duty aluminum foil) that fits into the gel frame of a Leko-type light.
If you want to play with it, you would need to add a small strip of tape at the edge of each diode. Once you figure out where and how wide to make the mask, you could make a more permanent version from an aluminum pie plate (or maybe even cardboard). That would let you make several in advance, and attach them as needed. It would be a PITA, but if you have the time, it is cheap to try. Good luck.