Some thoughts:
Emilidis was able to create sorcerous objects that were immune to Chorae because, as noted in the glossary, Emilidis was all about recreating "patterns in nature" or something along those lines. Spirals, octagons, etc. Of course, in Earwa, the patterns in nature aren't random coincidence, and indeed they have intrinsically metaphysical qualities. In other words, it's not sorcery at all really. If anything it's close to the Psukhe, in terms of its application/nature. In a world of meaning, you don't actually need sorcery (which disrupts the Onta) to create "magic", you just need to focus in on the right (or rather most potent) forms of this intrinsic meaning, which is basically intersubjective concepts that have meaning whether there are people around to give them meaning or not. For us, a hundred dollar bill only has value because everyone decided it does. In Earwa, that value exists regardless (not the best analogy but it's a start).
Not sure if it was mentioned, but Emilidis also made the octogonal "fire-scrying" rings, one of which is used by Kellhus.