John Anderson (aka psychic, the lead on the CakePHP Cookbook project) mentioned that he had a plugin I could use. He also provided a link to an experimental CakePHP plugin server he's setup and asked people to play around with. That PayPal plugin was one of the ones being offered.

This PayPal plugin is one of many housed on the server. There's also a client script that can be used on the command line to fetch and upload plugins to and from the site.