accidentals in augmented unisons

[luis jure]

hello list,

i'm using an example from the learning manual to write a chord with an
augmented unison:

naturalplusflat = \markup { \natural \flat }
     \relative c'' {
       \once \override Accidental
         #'stencil = #ly:text-interface::print
       \once \override Accidental #'text = #naturalplusflat
       \once \override Score.AccidentalPlacement #'right-padding = #1.5
       <b bes>
     }

this works, but i'd like to control the horizontal position of the
natural and flat symbols. i have no idea how i can achieve this, any
help would be greatly appreciated.

best,

lj