How about:
\version "2.19.47"
#(define (new-centered-mmr-stencil grob)
(let* ((sys (ly:grob-system grob))
(X-extent (lambda (q) (ly:grob-extent q sys X)))
(left-bound (ly:spanner-bound grob LEFT))
(left-bound-X-length (interval-length (X-extent left-bound)))
(left-bound-coord (ly:grob-relative-coordinate left-bound sys X))
(right-bound (ly:spanner-bound grob RIGHT))
(right-bound-X-length (interval-length (X-extent right-bound)))
(right-bound-coord (ly:grob-relative-coordinate right-bound sys X))
(new-stil
(grob-interpret-markup grob
#{
\markup
\concat {
\general-align #Y #0
\override #'(thickness . 2)
\draw-line #'(0 . 2)
\hspace #-.2
\pattern #7 #X #-.2
\path #0.2
#'((moveto 0 0)
(lineto 0.5 -1)
(lineto 1.5 1)
(lineto 2 0))
\hspace #-.2
\general-align #Y #0
\override #'(thickness . 2)
\draw-line #'(0 . 2)
}
#}
))
(new-stil-X-length (interval-length (ly:stencil-extent new-stil X)))
(translate-value (- (+ (/ (- right-bound-coord left-bound-coord) 2)
(/ left-bound-X-length 2))
(/ new-stil-X-length 2)
(/ right-bound-X-length 2)))
)
(ly:grob-set-property! grob 'stencil
(ly:stencil-translate-axis
new-stil
translate-value
X))))
{
\compressFullBarRests
R1*32
\override MultiMeasureRest.after-line-breaking = #new-centered-mmr-stencil
R1*71
}