Multiple simultaneous time signatures vs. staffgroups

[James Harkins]

Hi, I'm working on a trio. In one section, one instrument will play
metered music and the other two will have aleatoric notation, without
barlines.

LSR #344 [1] ("Printing music with different time signatures") shows
how to suppress normal barlines in one or more parts. But, in this
case, the staff with differing time signatures is not in a staff
group, and I wanted all three instruments to be in one staff group. I
modified the snippet (attached) to take the \new StaffGroup out of the
Perkussion variable and put it into the \score. Lilypond handles this
well -- except for one small detail.

At the end of the system, if one of the parts is in the middle of one
of its bars, the barline *within* the staff is suppressed. But the
StaffGroup barline extends from an adjacent staff to the outer edge of
the different-signature staff (image).

Is there any way to have the percussion barline extend only through
its two staves, and not touch the clarinet staff?

Thanks,
hjh

[1] http://lsr.dsi.unimi.it/LSR/Item?id=344

barlines-and-staff-groups.ly
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staffgroup-barline-oops.png
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