Add mode-specific-pair for emacs-lisp-mode

I'd like `t` to switch with `nil` in `emacs-lisp-mode`.

This used to work, but the alist refactor has removed this ability. I could add a hook to emacs-lisp-mode to modify `bool-flip-alist`, but it would be nice if bool-flip had a generic facility for mode-specific booleans or worked out-of-the-box with elisp.

What do you think would be the best approach?