Shorten volta spanner to first and last measure only

[Vlado Ilić]

I see there is a

\set Score.voltaSpannerDuration = #(ly:make-moment 3/4)

but it only prints the volta spanner on the beginning of alternative music, is it possible to print it also on the last measure of alternative?

For example, if i have 28 measures of alternative music, only to print volta spanner on measure 1 and measure 28