Split markups above and below spanner possible?

[Nick Payne]

With the following, where a textspanner terminates on the same note 
where there is also a trill indication and a barring indication, is it 
possible within the one voice to get the trill below the spanner and the 
barre above.

I achieved it in the end by creating a separate hidden voice and 
attaching the barring indication there with a different 
outside-staff-priority, but I was wondering if it is possible without 
the extra voice?

\version "2.13.30"

string = #(define-music-function (parser location stringnum dirn shorten 
adjBreak adjEnd)
    (string? number? pair? number? number?)
#{
    \once \override TextSpanner #'outside-staff-priority = #$osp
    \once \override TextSpanner #'bound-details #'left #'text = \markup 
\bold { \teeny \concat { \circle { \finger $stringnum } " " } }
    \once \override TextSpanner #'font-shape = #'upright
    \once \override TextSpanner #'direction = #$dirn
    \once \override TextSpanner #'dash-period = #0.8
    \once \override TextSpanner #'dash-fraction = #0.6
    \once \override TextSpanner #'thickness = #0.8
    \once \override TextSpanner #'bound-details #'right #'text = 
\markup { \draw-line #(cons 0 (/ $dirn -2)) }
    \once \override TextSpanner #'bound-details #'left 
#'stencil-align-dir-y = #CENTER
    \once \override TextSpanner #'bound-details #'left #'padding = 
#(car $shorten)
    \once \override TextSpanner #'bound-details #'right #'padding = 
#(cdr $shorten)
    \once \override TextSpanner #'bound-details #'right-broken 
#'padding = #$adjEnd
    \once \override TextSpanner #'bound-details #'left-broken #'X = 
#$adjBreak
    \once \override TextSpanner #'bound-details #'left-broken #'text = ##f
    \once \override TextSpanner #'bound-details #'right-broken #'text = ##f
#})

\relative c' {
    \stemUp c''16 \string "2" #UP #'(0.25 . -1) #7 #0.5 
bes\startTextSpan gis a <gis d 
e,>4\stopTextSpan\trill^\markup\small\upright { CVII }
}

Nick