The suggested feature are two keywords "nooutliersabove" and "nooutliersbelow" for "set style boxplot."
The "nooutliersbelow" keyword would omit outliers that are below the lower "whisker" edge; while "nooutliersabove" would work analogously.
This has been useful to me because I was interested only in large values of certain data, and not lower values.
I have added these changes to gnu plot 4.6.0 (see attached patch), but I don't think I diff'ed against the right old files. Each diff line in the patch reads
'diff -Nau -x '*.o' -x '*ake*' src_orig/graphics.c src/graphics.c'
The existing keywords "outliers" or "nooutliers" continue to work under this patch, of course.
If someone could tell me the exact patch format (old and new filenames/directories), I could update this. Or you could sed 's/src_orig/src_cvs' to fix the patch. This is my first contribution to gnuplot (or any open-source project).