Overlay "ossia" voice

[Mark Knoop]

I'm trying to create something a bit like an ossia voice which should be 
overlaid on top of the principal voice, but without affecting the layout of 
each; i.e. ignoring all collisions.

In the following example, ideally the Dots and Ties on the Gs in the first line 
should have the same positioning as on the second.

It's mostly working, except for the Dots which don't seem to have an equivalent 
property to NoteColumn.ignore-collision. Any thoughts on this?

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\version "2.19.82"

dimNotes = {
  \override NoteHead.color = #grey
  \override Stem.color = #grey
  \override Dots.color = #grey
  \override Tie.color = #grey
  \override NoteColumn.ignore-collision = ##t
}

{
  \time 3/4
  R1*3/4
  << {
    g'2.~
    \temporary \dimNotes
    2.~ 2.~ 2.~ 2.~
    \undo \dimNotes
    2.
  } \new Voice \magnifyMusic #5/7 {
    \override NoteColumn.ignore-collision = ##t
    \tweak NoteHead.transparent ##t
    \tweak Stem.transparent ##t
    \tweak Dots.transparent ##t
    g'2.\glissando
    aes'\glissando
    des'\glissando
    ges'\glissando
    b'\glissando
    \tweak NoteHead.transparent ##t
    \tweak Stem.transparent ##t
    \tweak Dots.transparent ##t
    g'
  } >>
}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

--
Mark Knoop