If Lily 34 (which I don't have yet) accepts
\score { \notes{ c8 c c c \times 2/3 { c c c c c c }}}
beamAutoEnd_8 = "1/2";
beamAutoEnd_12 = "1/4";
to produce
------- ----- -----
c c c c c c c c c c
or
\score { \notes{ c8 c c c \times 2/3 { c c c c c c }}}
beamAutoEnd_8 = "1/4";
beamAutoEnd_12 = "1/4";
to produce
--- --- ----- -----
c c c c c c c c c c
then you've already done what I'm suggesting.
I'm also suggesting that Lily accept
\score { \notes{ c8 c c c c12 c c c c c }}
.....
for consistency.
John