I see this code in the source for the library (XML/Saxon/XSLT2.pm):
foreach my $path (qw(
$classpath = $path if -e $path;
last if defined $classpath;
It looks like it expects the jar file in one of those paths. If your jar file is not in any of those, go ahead and edit the source and add your path to the list. That's my guess anyway...
If I were to rewrite this, I would make it configurable via (at least) some environment variable, maybe SAXON_LIB_PATH or something...rather than just a hard coded list of paths