..from my experience..for instance for packages..one if the solutions is:
To create a real anchor point (rigid pont) at the point where your scope of work or delivery ends up..
so you your model ends up with an anchor..and the remaining part, which is not in your scope ends up with the same ancor
these anchor are also handy for shipping and hoisting the package(s)

Another solution is take/include in your stress model ..an overlap (which means include in addition to your own piping, a part othe piping with its supports, of the matching piping which is just outside your scope/boundaries, for guidance: include 5 to 6 rests and 2 guides + one axial stop )