how to install rmagick to a custom directory (gem)

So..you install rmagick as a gem and it goes to the right gemrepository, but that still doesn't work? I search for RMagick.rb and then added that path to the RUBYLIB path, thus
export RUBYLIB=$RUBYLIB:/home/rdp/i386/gemrepository/gems/rmagick-1.15.7/lib/
(in ~/.bashrc). Voila