From Magnar Sveen, the creator of the package expand-region, taken from his github:
Example:
Let's say you want expand-region to also mark paragraphs and pages in
text-mode. Incidentally Emacs already comes with mark-paragraph and
mark-page. To add it to the try-list, do this:
(defun er/add-text-mode-expansions () (make-variable-buffer-local
'er/try-expand-list) (setq er/try-expand-list (append
er/try-expand-list
'(mark-paragraph
mark-page))))
(add-hook 'text-mode-hook 'er/add-text-mode-expansions)
Add that to
its own file, and add it to the expand-region.el-file, where it says
"Mode-specific expansions"
Warning: Badly written expansions might slow down expand-region
dramatically. Remember to exit quickly before you start traversing the
entire document looking for constructs to mark.
I would say you could add "er/mark-paragraph" to the expand-region list, that should do it.