The only other approach I am aware of is
Settings -> Cellular -> Scroll down to the Use Cellular Data For: section -> Find the App Store icon, and toggle the switch to Off.
This will prevent App Updates from happening over Cellular.
Unfortunately what this also means is that you can't use the App Store *at all* when on Cellular, not even for browsing/buying apps.
Like you, I would like to use Cellular Data for iTunes Match and iTunes Radio, but not Automatic Downloads. I only want App Updates to happen when on WiFI, but I'd still like to be able to use the App Store (manually) from time to time on Cellular. Hopefully Apple will give us more granular control for this in the future. Because for now, what I've chosen to do instead is to disable Automatic app updates... and that's a shame.