Hi,
Another option would be to use Installed Builds for the PCBs of the Engine. You would need to move the project outside the Engine root. The main problem is that the tools are not built to handle the project PCBs separately from the Engine’s. That would also make the distribution and alignment of both PCB packages.
You do need a part of the engine source, ie the public headers, in order to build the project. This is another thing to consider. You wouldn’t save much by getting rid of the Private Engine code.
I would recommend that you stick to the current flow as building what you describe would require lots of efforts and the benefits don’t seem to be that much.
Regards,