pitched trill fingerings

[Jim Cline]

Hello, I would like to indicate fingerings for a pitched trill, and also 
be able to control where they appear.  The
\set fingeringOrientations = #'(left) is ignored in the trill context, and 
the fingering is ignored for the secondary note of the trill.  Any ideas?
regards, Jim

\version "2.20.0"

\relative c'' {
 \clef bass
  \set fingeringOrientations = #'(left)
    \pitchedTrill
  a,1*7/8-1\startTrillSpan bes-2 s8 \stopTrillSpan
}