sourcing external read-only constraints files from within the QSF file

Although it would be nice if Quartus could figure out whether constraint changes from the GUI should be applied to the parent QSF or a sourced QSF, I'm content with (and in my specific set of circumstances, prefer) changes being applied to the parent QSF. What I really want is to abstract all of my HW-specific constraints (device, pin, I/O timing, etc) from the application developers, so they can't "accidentally" change them and they don't have to sift through a QSF file that has thousands of lines of constraints that they don't understand or need to maintain themselves.