[OS X TeX] Multiple fonts using otfinst

[Theo Moore]

I am using otfinst to generate the necessary files so that pdftex can
use OpenType fonts (http://www.ece.ucdavis.edu/~jowens/code/otfinst/)
For example, I ran the program on the Minion Pro series of fonts. The
program generates some font files as well as a minion.sty file. And
then a simple

\usepackage{minion}
\begin{document}
This is now minion
\end{document}

gives me what I want.

My question is, suppose I wanted to have a different text for say,
figure captions. How would I, midway through the document, redefine
the font to use? For example, if I were using fontspec, I could simply
write

\fontsize{18}{20}\fontspec{Adobe Caslon Pro}
This is now a different font

But without fontspec, I'm clueless as to how these sort of things are done!