It currently is not possible to use fonts other than those built into the application. I created the following idea thread (feature request) for having this functionality added. Please add your vote and any comments you might have.
Try installing HiFont from the App Market. It installs fonts on your android that work across most apps. Open HiFont, slide over to the Local tab. It tells you how to install new fonts to the program. Just make sure the font you download is a .ttf file.