How to dynamically change target for unit tests in Xcode 7?

I have a project that has multiple different targets/schemes (~38 of them as of writing this question) and I am trying to get unit testing working properly across all of the different targets. I got things working with one target, and tried adding my testing target to all of the different schemes, but it looks like when tests run for each scheme they actually run on the same, original target.

Looking in the project file I see that there's a specific Host Application associated with my testing target, and in the build settings the Bundle Loader and Test Host point to that same Host Application.

Is there any way to override those values for each scheme to run the tests against the current scheme's build target? Or some other way to set up a single test target to run across multiple build targets?