%%%%%%%%%%%%%%%%%%%%
simile = \markup {
\combine \translate #'(0.3 . 1.5) \draw-circle #0.2 #0 ##t 
\combine \translate #'(1.7 . 0.5) \draw-circle #0.2 #0 ##t 
\rotate #90 \translate #'(0 . 2) \beam #2 #-1 #0.5 } 

percentCN = 
\once \override ChordNames.ChordName #'stencil = #(lambda (grob) 
(grob-interpret-markup grob simile))
%%%%%%%%%%%%%%%%%%%%

harmonies = 
\chordmode { c1 g1 e1:m \percentCN e1:m \percentCN e1:m a1:m bes1 c1 }

\score {<< \new ChordNames { \set chordChanges = ##f \harmonies } >>}