Maybe something along the lines of a tobacco stuffer with the metal tube, but I would imagine it would get gummed up in no time. At least with oils, it's viscous and not sticky, but ground up bud is never easy to work with, especially in quantity IMO. Good luck, but I think a solution is out of my league.
Edit - if you have a specific geometric shape in mind, I could probably quick design it so long as the shapes aren't too complex, but other than that, I have no ideas that I think would work for stuffing small quantities of ground bud into gel caps.