I am assuming though, from the lack of answers back, that there appears to be no way to have org-mode grok markdown code blocks (triple backticks) when it parses as a substitute for `#+BEGIN_SRC` ?
I am no expert in the Org internals, but a quick search shows the strings BEGIN/END_SRC are hardcoded in a few places, so it seems to me you are correct, there's probably no easy way to do this.
--Diego