I should have mentioned this above, but using <a href="<?php the_permalink(); ?>"> didn’t work. I figured that was because the code is already inside of a <?php ?> tag, though.
I’ve found Big Door, which I think will do what I need:
http://publisher.bigdoor.com/
Does anyone have any detailed documentation on how to call the API for this? I’m not too familiar with PHP, but don’t want to use their mini-bar or WordPress widget, due to limited content.