subdividing sixteenth-note triplet beam groups

[Steve Yegge]

I would like this:

  \times 2/3 { c16 c c c c c }

to render with two beamed groups of three notes each, with the two groups connected by a single beam, like so:

c c c  c c c

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I have tuplet numbers and brackets set to transparent.

I tried #set subdivideBeams = ##t and then played with various settings for setting beatLength.  None of my guesses had any effect on the beam grouping, and all of them gave me warnings like these:

warning: cannot find property type-check for `beatLength' (translation-type?).  perhaps a typing error?

warning: doing assignment anyway

Is there a way to accomplish the beam subgrouping I'm looking for?  I'm running 2.16.0.

-steve