I have released rb_hijack-0.1, and it is now packaged as a rubygem to make my life easier, and to make it really simple to install and remove if you wish to
I have written Ruby bindings for libhijack. It isn't a complete implementation of the libhijack API, but it will provide you with the means to attach to a process and inject some shellcode to a PID that you supply from inside Ruby.
It is written as a module, so you can easily mixin it's functionality into your own module or use the module on its own.
Fetch libhijack from http://www.retoros.org
git clone git://github.com/robgleeson/rb_hijack.git rb_hijack-0.1
gem install hijack-0.1.gem
Ruby 1.9.1 support
The extension has been tested on 1.8.7, and 1.9.1.. Works on both.
Stable source available at http://www.github.com/robgleeson/rb_hijack/tree/rb_hijack-0.1
Development source available to browse @ http://www.github.com/robgleeson/rb_hijack/tree/master