Yes you can put Epsom Salts in empty capsules. This is the way I have to do it and it works great. I'm actually going to flush today. It takes about 15 or 20 to make a teaspoon but to me it is worth it. Otherwise I have a really hard time getting it down, especially the morning doses, and those are really important.
Ive done 8 or 10 flushes, and my most successful have been using epsom capsules. Ive tried Mag Citrate, Oxypowder , all that stuff. Nothing works as good as Epsom Salts if you can find a way to get it down. The making of the capsules is a little tedious, but worth it in the end.