In the 0.4.7 release, there's no way to add custom key binding as the GNU Readline defaults and a set of hard coded bindings are used.
I've done some work for the next release which is available in the master branch, which allows specifying custom bindings for profanity functions (window navigation etc)
https://github.com/boothj5/profanity/issues/687If there's any more bindings you'd like available, let me know.