I know that my reader is a “budget” model, but I’m cheap and I love this device. But this is a general problem with browsers too: code in a @pre@ tag overflows the layout unless told to scroll. As far as I know the PRS-300 cannot scroll.
So, could the ePub file get generated with a @code@ tag instead of a @pre@ tag? This way the whitespace will be preserved, but wrapped on smaller readers.