[CentOS] How to downgrade gtk2 libs in CentOS 6.8?

Hi all. I'm using a CentOS 6.8 VM to do volunteer builds for an open source project. I want to build Pale Moon with a gtk2 library older than 2.24, to allow people with older linuxes to run it. Short summary, if built against version gtk2-2.24 and/or higher, the binary will use a function that does not exist in gtk2-2.23 and lower. Net result is that the program dies with an "undefined symbol:" error for people with machines lower than gtk2-2.24. Yes, before you ask, they do get security fixes backported.

The hits from my Google search suggested...

yum downgrade gtk2

The response from yum was...

Only Upgrade available on package: gtk-2.24.23-8.e16.i686 Nothing to do

Are there ways around this?