[PyMOL] best way to rotate molecular bonds without dihedral context?

Hello, PyMOL users!

I am trying to figure out within the Python interface how to rotate the
parts of a molecule on one side of a bond about that bond's axis, given
only the two atoms defining the bond and a angle to rotate by (that is,
without requiring me to specify four atoms and a final dihedral angle
value as required by set_dihedral). While I understand the "rotate"
function, I can't figure out how, in the Python interface, to select the
atoms on one side of a bond given the bond's two defining atoms.

I've looked through the PyMOL C++ code, and it appears that this
functionality is provided by the layer3/Selector.cpp function
"SelectorSubdivide" when its "bondMode" flag set to true and given two
atoms; set_dihedral's C++ implementation seems to use this functionality
to select the atoms it will rotate. I tried to look through the rest of
the source to see if this selection behavior was somehow exposed to the
Python interface, but as best as I could tell it doesn't seem to be.

If anyone can work out a good way from the Python interface to select the
atoms of a molecule on one side of a bond, or if there is a
Python-accessible function that acts similar to set_dihedral but rotates
about any bond by a given angular change without requiring a bonded
sequence of four atoms to define an arbitrary dihedral plane (and an
otherwise unnecessary call to get_dihedral to to calculate the change
needed to know what angle I would need to give set_dihedral), I would be
very appreciative.

Thank you very much for your time!

-John