Though I was advocating this as a possibility, I should point out that he might include some actual punctuation in the cipher as well as the standard 26 charact

Though I was advocating this as a possibility, I should point out that he might include some actual punctuation in the cipher as well as the standard 26 characters, so it's still possible that it's just a substitution cipher. Additionally, it's possible that some of these characters aren't characters at all, but common repetitions. I'm thinking particularly of those slashes and backslashes.