I went to Pidgin's settings directory and created a .fonts directory to put the fonts in, but the font didn't appear in Tools->Preferences->Conversations->Conversation Font.
I've also tried moving GTK to \PortableApps\CommonFiles\GTK and I edited GTK\etc\fonts\fonts.conf to add this line:
I then put the fonts in \PortableApps\CommonFiles\GTK\share\fonts. But that didn't work either (Pidgin ran but the font didn't appear). I wanted to do this because I wanted to use the GNU Unicode font (http://unifoundry.com/unifont.html) without having to install it in c:\windows\fonts.
Both methods above worked for Gimp Portable btw with the same font.
I'd like to make a correction. Both methods did not work for Gimp Portable. Only the first method worked. I got confused because of the two other methods that did work for Gimp. One was adding the extra <dir> line on Gimp's GTK fonts.conf file. The other was copying GTK off pidgin to CommonFiles as is (no extra <dir> line), removing GTK from Gimp and still using the .fonts subdirectory in Gimp's settings directory.
In the upcoming 1.6 platform release, you'll be able to use portable fonts that work with all your apps. This will be the official way of using fonts portably rather than various hacks and switches in all the different apps individually.
Sometimes, the impossible can become possible, if you're awesome!