This is very cool! I remember wanting to do something like this, but did not know the tools you mentioned existed. I ended up using FontForge and deleting glyph ranges by hand through the gui. If I recall correctly, it worked. I really wish I had documented that!!
How does this work with a CDN? You're telling the host what data to send over?
Google Web Fonts, for example, lets you choose a subset of the font you intend to use so that the font includes only, e.g., the so-called "Latin-1" characters, and not all of the extended characters.
This data should be communicated through URL, like this:
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