Left deb as default but now you can 'make rpm' if that's your kink.
Wurks gud, (though your jdk dependency may vary):
[eric@leterel ~/fpm/jruby]$ rpm -q --requires -p jruby-1.6.1.noarch.rpm
jdk >= 1.6.0
rpmlib(PayloadFilesHavePrefix) <= 4.0-1
rpmlib(CompressedFileNames) <= 3.0.4-1
[eric@leterel ~/fpm/jruby]$ sudo rpm -Uvh ./jruby-1.6.1.noarch.rpm
Preparing... ########################################### [100%]
1:jruby ########################################### [100%]
[eric@leterel ~/fpm/jruby]$ /opt/jruby/bin/jruby -e 'puts "hello world"'
hello world
