Combining percussion parts in one staff

[Christopher R. Maden]

I’m engraving a marching band score.  The pitched instruments were fun. 
Percussion is giving me a headache, though.

Each drum has its own part, e.g.:
% bass.ily
\version "2.18.2"
bassMusic = \drummode {
  bd4 \f r bd r |
}

% bass.ly
\version "2.18.2"
\include "bass.ily"
\score {
  \new RhythmicStaff = "bass" {
    \bassMusic
}


% snare.ily
\version "2.18.2"
snareMusic = \drummode {
  r4 sn \f r r |
}

% snare.ly
\version "2.18.2"
\include "snare.ily"
\score {
  \new RhythmicStaff = "snare" {
    \snareMusic
}

In the whole-band score, I’d like something that comes out like:

% score.ly
\version "2.18.2"
\score {
  \new DrumStaff = "percussion" {
    bd4 sn bd r |
  }
}

If I try just parallel parts like this:

% score.ly
\version "2.18.2"
\include "bass.ily"
\include "snare.ily"
\score {
  \new DrumStaff = "percussion" <<
    \bassMusic
    \snareMusic
  >>
}

... I get rests scattered all over the place, not to mention redundant 
dynamics.  Is there a way to combine the different drum parts on one 
staff without engraving a terrible mess?

Thanks in advance,
Chris
--
Chris Maden, text nerd & chanteyman
<URL: http://crism.maden.org/ >
<URL: http://music.maden.org/ >
“Send these, the homeless, tempest-tost to me...” — Emma Lazarus