Everything is from CentOS including the kernel sources. I downloaded the SRPM and modified the spec file to %define buildsource 1 then did an rpmbuild. Then I installed the kernel-sourcecode rpm that it generated. So then I could run the kernel config from /usr/src/linux-<version> and then build a custom kernel.
I think that's one of the hardest ways possible to do what you want, and it may very well not work.
1 Install kernel src.rpm 2 run rpmbbuild -bp kernel.spec to get kernel source tree. 3 copy $BUILDSOURCEDIR/linux-config-for-your-arch.config to $BUILDDIR/.config 4 run make menuconfig (or xconfig or however else you want to do it. ) save config 5 copy config back to where you got it from, with the original name. 6 run rpmbuild -bs kernel.spec 7. rpmbuild --rebuild resulting kernel-src.rpm with --target=arch (i686, x86_64) 8 install resulting kernel rpms.
rough steps, but that should be pretty much what you need to do.