It is easy to do manually - i.e. got to the ~/.cpan/build/<dist> directory and run:

perl Makefile.PL INC="-I/usr/X11R6/include/X11"
make
make test
make install
[download]

and everything should be alright. See the documentation on ExtUtils::MakeMaker for more on the options for the Makefile.PL

/J\