\version "2.16.2"

stemOff = { \override Staff.Stem #'transparent = ##t }
stemOn  = { \revert Staff.Stem #'transparent }

Melody = {
  \key e \major
  \relative f' { e4 fis gis b }
  \improvisationOn \stemOff
  b'4 b' b' b'
  \stemOn \improvisationOff
  \relative f' { fis4 gis a cis }
}

Chords = \chordmode { bes1:maj7.5- }

\score {
  <<
    \new ChordNames \Chords
    \new Staff \Melody
  >>
}

% this works, but transposes E major to an unfortunate C# major
\score {
  <<
    \transpose ees c' \new ChordNames \Chords
    \transpose ees c' \new Staff \Melody
  >>
}

%{ So I did this to get Db major (five flats instead of seven
sharps) but now the chord symbol is not transposed correctly.
Granted, even the "correct" answer of aeses:maj7.5- is not all
that great, but the transposed output shows a very different
chord nomenclature.  It would expect it to say A double-flat
triangle flat 5.

Be that as it may, what's the practical approach to fixing that
one chord in the transposed output?  The original key of E
calls out a bes:maj7.5- so I think in Db the best choice is
g:maj7.5-.  How do I accomplish that?  A special-case Ignatzek
exception or some such?  Is that the simplest way?  %}

\score {
  <<
    \transpose dis c' \new ChordNames \Chords
    \transpose dis c' \new Staff \Melody
  >>
}