What you need to do is place the library folder (from vanilla processing) in a libraries folder (under PythonMode), on linux this is sketchbook/modes/PythonMode/libraries/peasy/library/peasycam.jar.
The latest python processing way of calling libary is as for vanilla processing to use the processing menu add library method, which adds the following to your sketch
add_library('peasycam')
I have since updated many more of my
processing.py examples to run using the latest python mode in the processing ide.