Embedded asterisks seem work here, but with poor compatibility. It does not seem to be one of widely-supported common features of markdown. It does not work in my offline markdown editor. It does not work in some other sites (as where the workaround comes from).
Since bitbucket wiki can use only a relatively small subset of markdown syntax, to keep editing simple, I set up rules to require the documents fit to the subset and expect other environments would fully support that subset. Then I can edit online or offline as I need, with few risks breaking the code displaying elsewhere by occasional use of some syntax only well-supported in the wiki. I don't want to make it more complicated. I also don't want to add more restrictions to make sharing the .md code harder.
I know inline HTML is not likely to be supported for several reasons. But please reconsider to add support of some limited forms where it cannot be a security hole.