What I could use are zips for moving CM7/9 from primary to secondary partitions on EMMC, and vice versa. There are several such zips for stock, but none that I have found for CM. Make a set for each of this build's SD partition sets, too, and we non-coders can update, back up, and restore our builds without any need for doctored update zips or custom CWM (though you would need to be willing to temporarily remove whatever's on the primary EMMC partitions).
Here's an example of a set for managing two stock builds on EMMC:
I don't know what these zips do in terms of renaming boot files or changing init.rc, but I could not get CM7 or CM9 to boot from Alt with these.
While I'm more interested in an internal dualboot, the same strategy could be applied to this SD build by making a similar pair for each SD partition:
copySDPri2Pri
copyPri2SDPri
copySDAlt2Pri
copyPri2SDAlt
That way, users could update, back up and restore using standard CM zips and CWM functionality, wouldn't need to be spoonfed altered zips, and wouldn't be left in the cold when no one felt like doctoring CM updates anymore.
Granted, I have no idea how trivial/challenging it is to make such files