Installing files outside /usr/lib/ruby/ using rubygems

Hello to everyone.

I'm writing an application using the KDE ruby bindings and I'd like to package
it as a gem. However, for the application to integrate correctly with KDE, a
file with extension .desktop needs to be installed in one of the directories
contained in the KDEDIRS environment variable (on my system, for example, they
are /usr and /usr/local). As far as I could understand reading the rubygems
documentation at (since that page documents rubygems 0.8,
however, I don't know how much of it is still valid), rubygems installs all
example /usr/lib/ruby/gems/1.9.1/gems/myapplication-1.0.0). Is this correct?
If so, isn't there any trick at all allowing me to force it to install the
.desktop file somewhere else?

If I can't install the .desktop file in another directory using rubygems, then
I can only see two other options. The first is to tell the user to add the
directory where rubygems installed the application to the KDEDIRS environment
variable; the second is not to use rubygems and to package my application
using something else. I don't like any of these approaches. Setting the
environment variable means more work for the user and needs to be done every
time a new version is released, since the version number is part of the name
of the directory installs it. Using another packaging system (my choice in
this case would be using CMake, which is the build system used by KDE itself)
would force the user to manually install the gems my application depends on,
again meaning more work for the user. What do you think?

Thanks in advance