Beam angle with whole-note tremolos

[Knute Snortum]

Hi everyone.

I've run into a problem that seems to be an old issue: the angle of
the beams between a whole-note tremolo is horizontal, but should be
tilted slightly.

https://gitlab.com/lilypond/lilypond/-/issues/318

My question is how to fix this in the source file.  Is there a way to
manually adjust the tilt of a beam? I suspect there is but I'm having
no luck finding it. Or maybe there's another way to get around the
problem. Any suggestions are welcome.

--
Knute Snortum