Hello.
Unfortunately, there is no way. SpaceX has not implemented any advanced settings. And I can't see their willingness to do this.
I can recommend using a better 3rd router with all the required functionality.
Switch the Starlink router to bypass mode (you can do it in the Starlink app). Connect your router to the Ethernet port on the Starlink router.
Configure your router to WAN Auto IP/DHCP. Add a static route to 192.168.100.1.
That's all.
Your custom router will provide you access to the internet as soon as the Starlink dish is connected to satellites.
The Starlink app will work normally. It only requires this static route to 192.168.100.1