Unless I'm missing something specific,
I think this is based on a misunderstanding.
Help files, as from Stata 7, are based on
SMCL, and there is no fixed, pre-defined line width,
although there can be, and often are, fixed
new paragraphs.
Rather the issue is to size your window
so that what is copied and later printed
is the right size.
This issue is surely part of the general issue of saving reproducible
windowing preferences. With the present technology (correct me if I'm
wrong), if you want the printed lines from the Help window to be the right
size for your printer, then you have to tweak the window size by trial and
error, typically wasting a bit of paper in the process, and then use the
menu sequence