Moving a single note (optical spacing once more)

[Urs Liska]

As discussed recently (starting here:
http://lists.gnu.org/archive/html/bug-lilypond/2015-11/msg00054.html)
LilyPond's optical spacing can have side-effects. If you consider the
first attachment you can see that the quavers of the left hand are
spaced irregularly because LilyPond moves the fourth note of each
semiquaver group slightly to the left.

As we have discussed optical spacing can be prevented with
    \override SpacingSpanner.uniform-stretching = ##t
as you can see in the second attachment.

If I do this I sometimes have the situation that I need more space
between the fourth and the fifth note, as you can see from the third
attachment.

It is possible to give the fourth note some extra space through
NoteHead.extra-spacing-width, but this spoils the regular spacing of the
quavers again (fourth attachment).

What I would like to achieve is moving just the fourth note a little bit
to the left, as if just this note were optically spaced.

However, no combination of NoteHead.extra-spacing-width or
NoteSpacing.same-direction-correction, applied to the fourth or third
note, seems to have any effect.

How could I achieve what I need?

Thanks for any suggestions
Urs

uniform-stretch.png
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uniform-stretch.png
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uniform-stretch.png
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uniform-stretch.png
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