There is no single ROS tarball, because ROS is a messaging library at its core, but hundreds of robotics libraries as well.
The core sources of ros are ros and ros_comm
In principle they are build using cmake (not maketools like many other projects you know), but for various reasons they still require the catkin build tool.
https://github.com/ros/catkin
To just install the ros and ros_comm packages from source, you will not need other ros-specific tools, I believe. However you would still miss many important ROS libraries and tools (E.g. action lib and tf).
As gvdhoorn explained, your best hope is to look at the installation instructions for other Linux variants, I think the ones for Groovy on Gentoo use no specific package manager for ros-related stuff:
http://wiki.ros.org/groovy/Installation/Gentoo
Another possibility for you is to try ros as provided by robotpkg
Also, it is very likely many people did not see this question due to the tags you used, I'll try to improve my tag filter, as I don't know what other tags you would have put in.