overlapping notes transcribing to tablature

[Marten Visser]

Hi, I'm trying to create tablature for guitar from regular notes. I 
have a piece with chords and melody, formatted for a piano staff.

For conversion to tablature, Lilypond guesses the string and fret to 
play the note on. This may lead to two or more notes on the same 
string on different frets at the same time. In such cases, the 
fretnumbers appear on top of one another.

I use these transcriptions and give them to a guitar player, who will 
then seek out what will be good fingerings. Unfortunately, when the 
fretnumbers are printed on top of one another, he can't see them and 
so he can't transcibe them or he'll need to read the regular notes, 
which is difficult for many (amateur) guitarists.

Is there a way to get lilypond to write simultaneous notes on the 
same string next to one another, separated by a comma or so?

Example:
===========================
% Example: Overlapping notes on tablature

\version "2.12.0"

% ------------------- Notes ----------------------
musicalContent = #(define-music-function (parser location) ()
#{
        c4 a' <c, a'> <a' c,> |
#})

% ---------------- Typesetting -------------------
\score { <<
        \new StaffGroup
                <<
                \new Staff = "regular"
                        <<
                        \relative c'' \musicalContent
                        >>
                        \new TabStaff = "tablature"
                        <<
                                \relative c'' \musicalContent
                        >>
                >>
        >>
}
===========================

Example shows fret 8 and 17 on top of one another, resulting in 87 or 
17, depending on which one is printed first.

Entering the fretnumbers manually is explicitly not an option, as I'm 
not a guitarist, and lilypond's transcription to tablature is the 
starting point for the proper fingering for the guitarist I work together with.