Split stem for different pitches on same staff level

[P Scott Horne]

In the key of D-flat major, I wrote

        <d,16 bes'> <a' aes> <d, bes'>

and got for the middle chord two noteheads side by side, preceded by a
natural sign with a flat sign superimposed.

Aside the obvious error (presumably a bug) of superimposing accidentals,
this notation is incorrect.  Standard practice is to split the stem into a
Y-shaped one that connects both noteheads, each immediately preceded by its
accidental (if any).  Is there any way to achieve this effect in LilyPond?

Scott Horne