Customized ISO

Hi,
I'm trying to customize an ISO image of RHEL6.3/x86_64 Server, I simply need to add a few more packages during installation.
I'm doing the following:
-> mounting ISO image
-> copying content locally
-> modification of the xml file in Server/repodata
-> sorting xml with xsltproc
-> createrepo ...
-> mkisofs ...

All work fine, my new packages are added and installed when I test the new iso image ...
However, I need now to add also packages for i686 and this does not work. I tried with option arch='i686' in xls file like this:
e2fsprogs-devel

but this does not work -> x86_64 version of e2fsprogs-devel is installed instead.
Does somebody know a way to include/install i686 packages in an x86_64 distribution ?
Support send me to this page: https://access.redhat.com/site/solutions/2761 but does not seem to fit my needs.
Thanks in advance for you help,
Alain.