Barring any more complicated notation decisions—like slurs, ties, expressions, or polyphonic voicing—two much simpler, easier ways to implement this than the current answer would be the following:
ees1^\markup \italic \translate #'(3.7 . 0) "rit."
ees1*3/4 s4^\markup \italic "rit."
For number 1, it’s a matter of attaching the markup to the note, then shifting it to the right some arbitrary distance. (See A.11.2 Align)
For number 2, it’s a matter of scaling durations, using spacer rests, and attaching the markup to that spacer rest; specifically, tell LilyPond to assign the whole note 3/4’s of its duration value, and use the remaining 1/4 of the measure to insert a spacer rest and attach the markup there. (See 1.2.1 Writing rhythms)