A starting point is using clone-by-date.  This allows you to skip the individual approval process for errata.  This does mean you need to do this on a date basis, so you will be pulling everything into the engineering channel from the RHN base channel from then.  Once you start pushing up to the other clones, it's not such a big deal, you can use the engineering source. 

You also need to make sure that there aren't any updates pushed during your testing process, e.g. engineering is frozen until *after* the clone to dev.  Otherwise you run the risk of adding untested errata.

spacewalk-clone-by-date --username=demo-admin -l rhel-x86_64-server-6 ENG-rhel-x86_64-server-6 -d `date -d today +%Y-%m-%d`
spacewalk-clone-by-date --username=demo-admin -l ENG-rhel-x86_64-server-6 DEV-rhel-x86_64-server-6 -d `date -d 'next week' +%Y-%m-%d`

Change to your username and I've made up the target channel names.  Make sure to change the date strings too :).  You can use any date in the past, e.g. -d 2011-01-13 should get you everything as of the release of RHEL 5.6.

If you have a large number of channels and child channels, look into using a config file.  Here's a sample:

{
"username":"demo-admin",
"assumeyes":true,
"blacklist": {
              },
"removelist": {
              },
"channels":[
             {
                "rhel-x86_64-server-6":"dev-rhel-x86_64-server-6",
                "jbappplatform-5-x86_64-server-6-rpm":"dev-jbappplatform-5-x86_64-server-6-rpm",
                "jbappplatform-6-x86_64-server-6-rpm":"dev-jbappplatform-6-x86_64-server-6-rpm",
                "rhel-x86_64-rhev-agent-6-server":"dev-rhel-x86_64-rhev-agent-6-server",
                "rhel-x86_64-server-6-rhevh":"dev-rhel-x86_64-server-6-rhevh",
                "rhel-x86_64-server-6-rhevm-3":"dev-rhel-x86_64-server-6-rhevm-3",
                "rhel-x86_64-server-6-rhevm-3.1":"dev-rhel-x86_64-server-6-rhevm-3.1",
                "rhel-x86_64-server-ha-6":"dev-rhel-x86_64-server-ha-6",
                "rhel-x86_64-server-optional-6":"dev-rhel-x86_64-server-optional-6",
                "rhel-x86_64-server-rs-6":"dev-rhel-x86_64-server-rs-6",
                "rhel-x86_64-server-supplementary-6":"dev-rhel-x86_64-server-supplementary-6",
                "rhn-tools-rhel-x86_64-server-6":"dev-rhn-tools-rhel-x86_64-server-6"
             }
           ]
}