Breaking long lines in XHTML

Is there any support in the DocBook XSL stylesheets to break long lines in
XHTML? I know it sounds strange. As ePub files are based on XHTML and there
is no way to add a horizontal scrollbar (with CSS) to code examples with
long lines it's unfortunately a requirement. In my ePub files which I
created so far the long lines are simply cut off. Or does anyone know a
preprocessor (on Windows) to reformat source code automatically (the source
code is in separate files which are included)? 

Boris