\new RhythmicStaff {
  % Set tuplets to be extendable...
  \set tupletFullLength = ##t
  % ...to cover all items up to the next note
  \set tupletFullLengthNote = ##t
  \time 2/4
  \tuplet 3/2 { c4 4 4 }
  % ...or to cover just whitespace
  \set tupletFullLengthNote = ##f
  \time 4/4
  \tuplet 5/4 { 4 1 }
  \time 3/4
  2.
}