Yes, I am mapping subdomains.
But I'm afraid you've lost me.
Most sections under the general settings tab have a checkbox for "Apply the settings above to the entire network."
However, the relevant section in this case, "Network Security and Performance Powered by CloudFlare" does not have such a checkbox. (Note that this is different from the CDN section.)
Moreover, even if it did have such a checkbox, it isn't at all clear where I'd put in an API key or domain name (or any other settings) for individual domains.
Is it possible to network activate W3TC and use its CloudFlare functionality with multiple domains? And if so, how?