Melisma with manual syllable durations

[David Sumbler]

In 2 of the set of 6 songs I have (rather slowly) been setting, I want
2 sets of words: the original, and an English version.  In each of the
other 4 songs there is just one set of words.

After much experimentation and a lot of failures, I found a way of
doing what I wanted, which is to use manual durations.  This may very
well not be the best nor the simplest way of doing it, but it is the
only way I found that works.

The only trouble is, I cannot work out how to produce a melisma mark
when using manual durations.  The following snippet illustrates the
problem:

%%%%%%%%%%%%%%%%%%
\version "2.19.48"

\paper { ragged-right = ##f }

voice = { \time 3/4 \partial 8
          e'8 | e' d' d'4( ~ d'16 c') b8 | c'4 c'4. r8 \bar "|."
        }

words = \lyricmode { Ac er -- aill yn __ ei fe -- di. }

trans = \lyricmode { An8 -- oth -- er reaps4. __ the8 har4 -- vest.4. }

<<
  \new Staff { \voice }
  \addlyrics { \words }
  \new Lyrics { \override LyricText.font-shape = #'italic
                \trans }
>>
%%%%%%%%%%%%%%%%%%

The melisma appears as required in the upper set of words, but not in
the lower.  I have tried various ways to get what I want, but so far
without any success.

Can it be done?

David