Hummingbird - Browser Caching - turn on/off and refresh sub-site?

I have installed Hummingbird on a multisite. I was previously using WP Super Cache, so wanted to test out Hummingbird browser caching. However, there doesn't seem to be any way to turn on Hummingbird browser caching per sub-site.

I would like to:
1) Turn Hummingbird browser caching on or off per sub-site.
2) More importantly, how do I refresh the cache of a single sub-site? At the moment I am turning off browser caching and then on again - which affects the whole network.

Thanks
Josh