We currently do not have a feature like that, that is true.
When building apps, best practice is to use a dedicated (often local) dev instance. To test with multiple users / roles simultanously, we assign all test users admin permissions on the instance. This way they all can stay logged in while the Builder mode is active.
This of course works poorly in a production system, where the number of admin users should stay limited - and admin permissions should not be given to test users in general. In a dev instance, this does not matter and works well for testing.