Depending on your timeline or how much you want to live on the edge, there were some great improvements that are set to be introduced to 4.1 that I think will allow you to do just what you’re looking to do. If you want to live on the edge a little, you could develop with the 4.1 beta and switch to the release at the time of launch (be sure to file bug reports if you find them 🙂 )
Here is a link to the make post that goes into a bit more detail: https://make.wordpress.org/core/2014/10/20/update-on-query-improvements-in-4-1/