I painted the bottom of my flowers with a brush, but you could try one of two things:
1) mix salt with my concoction, put it in your mold, then add bomb mixture and U mold as usual.
2) if the salt gets visually ruined by being coated on all sides like above, take my mixture and halve the alcohol and polysorbate 80. I'd want just a little alcohol left tho since salt is water soluble. Let mixture cool till getting thick. Paint it onto the bomb, place salt there.