I'm assuming the answer is no but always better to ask. I was unable to find the functionality in the documentation for Packer. We have been using VMWare Studio with CentOS5.11 and with Studio, similar to anaconda, you can specify an RPM list to install from the ISO as part of our build system, e.g.
<vadk:OSPackages><!-- Additional OS packages needed by the ISV's application -->
<vadk:Package vadk:name="alsa-lib"/>
<vadk:Package vadk:name="audit-libs"/>
<vadk:Package vadk:name="authconfig"/>
...
</vadk:OSPackages>
We are transitioning to CentOS 7 because Studio has no support for anything later than RHEL 6/CentOS 6 and I have exhausted trying to get Centos 7 with Studio to work. So we are looking for another solution and like that Packer can produce VMs for multiple targets so it makes sense to move to Packer.