Performance testing without counting setup

I’d like to performance test the last step (step 3) of my checkout using
ActionController::PerformanceTest. Since these tests are based off
integration tests, my understanding is I have to run through steps 1 and
2 in the test before I can get to step 3 (unlike a functional test where
I can assign things in the session to fake steps 1 and 2). My question
is, is there a way to have the performance test only report metrics
related to checkout step 3? I don’t want the metrics to be tainted by
me going through steps 1 and 2 to get to step 3.