You can't embed a font in a MOBI. You can use a named font, but if it isn't on your system (and it won't be on a Kindle) you get the default font. In general, MobiPocket advises against trying to set the font in a MOBI because that way the reader can chose the font they like. On the Kindle, you always get the same font for MOBIs.
It is possible to convert TOPAZ to another format (which always requires circumventing the DRM as the first step), see
DarkReverser's Blog for more information. Monitor the latest comments for any recent updates. If you are interested in the TOPAZ format, see also
The Topaz DRM Creator has a Blog!