An easy way to do it? Well, not really. Particularly in the general case.
What you are looking for is someone providing a repository holding pre-compiled binaries for the versions of the packages you want to install, plus any needed dependencies, for the base system (CentOS 6.4) that you are using. This is often referred to as backports.
CentOS isn't supposed to be bleeding edge. It's a server-class distribution, sort of like Debian and RHEL (which it very closely resembles, to the point of aiming for 100% binary compatibility), and as such, favors version and configuration stability over new features. If you want the latest and greatest, you should consider other distributions; Fedora and Ubuntu come to mind as closer to what you might be after, and at least Ubuntu does offer a server version (though I'd expect that you can get to the same state starting with any Ubuntu install).
In your particular case, I would also question why you are trying to do this. If there is a specific issue in the CentOS-provided gtk+ binaries that is fixed in the most recent upstream version, opening a ticket with the package maintainer through the appropriate channel (usually a web-based bug tracker; I don't know exactly how CentOS does it) seems a better approach than trying to shoehorn in a library of a very different version than what the distribution-supplied software is built against and expects.
Note that due to code backporting, an earlier version number doesn't necessarily mean that a later fix has not been incorporated. That is generally how critical fixes are incorporated into all similar distributions: the relevant change in the upstream code is isolated and then incorporated ("backported") into the version provided by the distribution's package maintainer, and a new package is built and distributed.