I came up with a third boundary condition setup as follows:
Create a large plane geometry for the PCB to sit on
Place fixed support on the plane geometry (for the purpose of simulating the "ground" in a reflow oven)
Set a rough (or maybe frictionless?) contact between the ground plane and PCB (To allow a gap to form when the PCB bends)
However, this setup unfortunately did not converge when I tried running it. Any suggestion for improvement is appreciated!