According to man editrc, you have to put bind -v in your ~/.editrc file to enable vi-like mappings in software that uses editline. Which in its turn will allow you to press <Esc>v there to launch vi itself.
But is it possible to tell a REPL (I'm talking about python specifically if that matters) to launch Vim on that keypress, not vi? I have an old version of Vim 7.3 aliased under vi, which isn't exactly very helpful these days, but I still would like to keep it that way...
(Just in case, in Bash, it uses $EDITOR variable when launching an editor, and therefore works just fine.)