Inserting a space between certain notes in Lilypond

[Miller]

I've tried the documentation and various snippets, but I'm not having any luck 
with the following:

I'm trying to force extra spacing in between specific notes in Lilypond.  In 
general, the spacing is good.  However there occurs a sequence (in 4/4) time 
where a measure starts with a half note tied to an eighth note and then 
followed by a separate eighth note.  In the lyrics, this is the end of one 
sentence and the beginning of the next.

However, the second eighth note is very close to the previous tied half+eighth 
note.  I'd like to increase the spacing between these two notes to represent 
their phrasing more accurately.

(By default, Lilypond wanted to join the two eighths together with a beam, 
which was even more confusing.  I overrode that with \autoBeamOff...On)

The snippet is like this:
    b'8. b'16 b'4. b'8 a' g'
    \autoBeamOff fis'2( fis'8) 
    % Want space here
    \autoBeamOn d'8 fis' a'

This kind of sequence occurs frequently in the piece.  The overall spacing of 
the score is fine.  It's just occasionally that I want to make sure that 
there's a visual separation where indicated above.

I tried the following:
1. Overridding the SpannerSpacing common-shortest-duration - this increased the 
overall spacing, which made it look more spread out overall, but didn't fix the 
issue.
\layout \context \Score \override SpacingSpanner #'common-shortest-duration = #
(ly:make-moment 1 16)

2. Overriding the SeparationItem/padding... but this didn't seem to have any 
useful effect.

3. Using a spacer-rest, but this obviously took away beats from the measure, 
bumping following notes into the next measure.

4. Using a grace-note spacer-rest... but this didn't have any effect.
e.g: \grace s4 ...

Any other suggestions?