When I was using Portable OpenOffice.org 2.0.2, I followed the advice given in the link below in order to use truetype fonts not installed in the PC.
So, in OpenOffice.org Portable 2.0.3, I copied the same fonts in the closest directory I could find, which was the following:
2.0.3 - \OpenOfficePortable\App\openoffice\share\fonts\truetype
(note: compare to 2.0.2 - \PortableOpenOffice\openoffice\share\fonts\truetype)
However, none of the fonts which I copied now show up in font combobox in the format toolbar.