The two main options I see are as follows:
- Just have people do it in Unicode. It would probably be useful in that case to link to or create a nice repository of common symbols in the FAQs to facilitate entry. It is what Writes_in_IPA, a user on Reddit, seems to be doing.
- Look for/develop a LaTeX/tipa-style library to allow for entries like
\tipa{p\super hEt}
. The Mathematics StackExchange site very successfully uses Mathjax.