Right now, RWPaint uses fonts that are installed in Windows, so it does not load the fonts directly from files, but lets Windows do that. An extension that would allow usage of custom fonts will probably come, but it may take a while.
Plug-in suggestion
PortableApps fonts
Anyone here use PortableApps.com software? It's a suite of ... portable apps... yeah that's obvious... nevermind. But they also have a system so that you can have fonts saved to the flashdrive, so you don't have to install it on all the computers you use. Awesome-looking documents, no matter where you go! It can store any standard font file.
All that's missing to get Paint and the others to use it is the directory. Assuming you use Portable fonts and you put Paint in the same folder as your other apps, the fonts should be located in ../portableapps.com/data/Fonts . Is it possible to make a plug-in for Paint that can use this? That'd be awesome!
I do NOT know code, but the only other thing I can think of is that it would have to check if it's installed on a Portable Apps drive. That might be tough... :/ It would also have to be installed in Portable mode. P.A. platform doesn't stop the apps from leaving behind registry files, it just sets up a Start menu- type thing.