Thank you for the explanation @mraab
Unfortunately, as of now, the browser module can only be used in the iteration body.
From your explanation, it looks like your setup can be done completely away from the test implementation, as it does not pass any data to the iteration functions etc. If that is not an option, a workaround would be to use two different scenarios, one that would run the UI scenario, making sure that the server is configured properly, and one that would actually run the load test. See this post on how to run scenarios sequentially.
Let me know if that helps.