Break long programlisting lines without spaces?

Hi. I'm producing PDF and XHTML from DocBook using Saxon 6.5.5 and FOP 1.0.

Some of my programlistings include long lines of code or sample
output. I configured my customization layer to break long lines at
spaces as described here. It works wonderfully.

http://www.sagehill.net/docbookxsl/FittingText.html#BreakLongLines

The remaining long lines occur at unbroken strings of characters. I
have some that are long enough to spill off the paper in PDF. Is there
any way to break lines at spaces where they exist and then set a
maximum line length at which the line must be forcibly broken?

Has anyone developed a customization that will do this?

Thanks for your help.

Peter Desjardins