Page caching

I would love to be able to use this module, but there just doesn't seem any way I could turn off page caching and not have my site performance go downhill very quickly.

Is there a way to get around having to have page caching turned off? For instance, is there a way to force the cache to flush when someone switches between themes? Perhaps there is a way to lock in the theme on a mobile device using a cookie?

It seems that the only option to get around the page-caching requirement is to create a separate mobile site, which seems quite a drastic step. Any advice would be greatly appreciated. Thanks.