(defvar o (make-overlay 0 0 nil t t))
(minibuffer-with-setup-hook
(lambda ()
(set (make-local-variable 'face-remapping-alist)
'((default :height 1.3)))
(move-overlay o (point) (point) (current-buffer))
(let ((text (mapconcat
#'identity
'("Some" "text" "that" "will" "not" "fit"
"the" "minibuffer" "window")
"\n")))
(put-text-property 0 1 'cursor t text)
(overlay-put o 'after-string text)))
(read-string "Multiline\nprompt: "))
Is it possible to make the prompt visible? Should I file bug report for this?