Is there any way to make yum also download srpms for every downloaded (and installed) rpm?.

I just want to keep a repository of source files needed to build a system in any given state it currently is. For instance, I can download the srpms for the base system, but as time passes, the system will auto-download security fixes and other app updates... I'd love the srpms for each to be downloaded automagically and placed in, say /home/userX/source-updates/

how would you approach this? is it needed to patch yum? or RPM? or maybe there's an existing mechanism to accomplish this?

Thanks in advance...
FC