I'm writing a tool to build bitmap fonts for use with this very method. Instead of starting with a very high res version explicitly, you start by specifying the texture dimensions. The app then figures out the maximum pixel size per glyph to pack into the requested texture. Then, per-glyph, it uses FreeType2 to render a much higher res glyph (16x higher res), compute the signed distance field for that single glyph, then packs it into the texture.
The thread is here, and any feature requests are gladly accepted.