--blacklist option?

[edward-martyr]

I now have a page containing glyphs

U+20,U+21,U+23,U+27-29,…(omitted for concision),U+3C0,U+1ED2,U+200B,U+2014,U+2019,…(omitted for concision),U+1B165,U+218BF

Would it be possible to have an option --blacklist=U+00-U+2000 so that only glyphs after U+2000 are subsetted?
I'm using glyphhanger for a CJK font and would like Latin glyphs, except em dash, to be rendered using local fonts, so dividing by U+2000 is practical. If --blacklist=US_ASCII --whitelist=U+2014 is also supported it'd be a more elegant way.