Hello Martin,
I believe what you would like to do is performing several installations, but without running SWPM screens everytime. Please check the SAP note below:
950619 - Installation of SAP Systems with Unattended Mode
This SAP note explains that you basically run the first installation. Then you can use the file generated and use it to perform the other installations as well without using the GUI.
I hope this is what you were looking for.
Best Regards,
Henrique Girardi
SAP Active Global Support