How can I properly parallellize my test suites in TeamCity?

So I have a scenario whereby I have many different test suites. They are all triggered by a Create Test Environment step. However, these test suites cannot run concurrently on the same environment, as they would interfere with each other. To alleviate this, I added a shared resource in TeamCity and configured the build definitions to block on this resource, so that only one test suite runs at a time. This works.

However, if while the test suites for Environment A are running, another code change is checked in, Environment B can be created by the Create Test Environment step, and all the test suites are re-queued. Currently, due to the fact that they all share a shared resource that they block on, those tests then sit in the queue awaiting access to the shared resource. However, there is no reason that the tests for Environment B cannot run (one build at a time) in parallel with the tests for Environment A. How can I best tweak my TeamCity configuration to achieve this?