How do we select between multiple function call signals depending on a switch input?

Hello, I am trying to set up a Simulink construct that selects between multiple function call signals, which happen to be outputs of three separate black box subsystems. Normally I would have merged them as outputs of three separate enabled subsystems, but that isn't an option as the Merge block does not support function call signals. Is there a good way of doing this, without going into s-functions?