Currently we can set baseline branch using SonarQube Portal. It would better and flexible to pass this property as SonarQube/Scanner input parameter.
There are already a couple of other threads for this feature request (for reference this one, and this other one). And I see you’ve already posted on both of them.
It’s better to keep track of this request on the existing threads.
We took into account these requests and we plan to simplify the automation of projects creation, which should include the configuration of the reference branch.