Not sure about making your own LiveFonts… I feel like that isn’t an option, but I couldn’t say for sure.
You could get the effect you want manually though… just takes a bit more setup. Prep your title in Photoshop and chop it up thinking about shapes and strokes rather than letters. You could use animated masks or cropping to reveal each part in Motion.
Something like this will get a lot easier with Motion 3. You could animated a paint stroke and mask it with your original text object to give the effect that the text is writing on. Come to think of it, you could probably adapt something like specialcases’s drawing lines tutorial from motionsmarts.com along with a text mask to get the effect you’re looking for.
Zak