keep \bar subdivision out of full-measure rests

[Kieren Richard MacMillan]

[ Lilypond 2.8.1 ]

Hello, all --

I've got a subdivided bar (using \bar ":") which ends up cutting  
through full-measure rests in other (tacet) parts, e.g.,

What are my options for stopping this from happening? In other words,  
if the staff has no music in that bar, I'd like the global bar  
subdivision not to show up. [Worst case scenario, I'll separately tag  
the score (with individual rests per sub-measure) and part (with a  
full-measure rest)...]

Thanks,
Kieren.