beaming pattern question

[Jay Anderson]

I have this rhythm (in 6/8 meter): c8. c16 c c. So a dotted-eight
followed by 3 16ths. The default beaming pattern isn't quite what I
need. The last two 16ths are grouped and the first has a beamlet on
the left side. I want the 3 16ths grouped together. I have a couple
work-arounds:

c8.
\set stemLeftBeamCount = #1
\set stemRightBeamCount = #2
c16
\set stemLeftBeamCount = #2
c c

This is a lot of typing since this is somewhat common in the piece I'm
working on.

\set Score.beatLength = #(ly:make-moment 3 16)
c8. c16 c c
\set Score.beatLength = #(ly:make-moment 1 8)

However this seems to mess up the beaming of other rhythms.

I messed with adding an override-auto-beam-setting, but it doesn't
seem to be what I'm looking for. I also messed with beatGrouping, but
I couldn't get that to do quite what I want either. Is there a general
way to specify this rule? Thanks.

-----Jay Anderson