I came across this limitation myself recently too. Unfortunately the Presence values are used to initialize a non-uniform random number generator and this is done in an initialization process, so it cannot be changed dynamically.
I'm afraid there is not a solution that allows you to use the Randomise operator in this way, however please find attached a workaround that uses the Selector operator with an expression to create a similar effect.
It is generating a random number between 0.0 and 1.0 and checking if that is more or less that the segments current position along the X Spline. IF it is greater it will add a perforation and if less a solid segment .
I hope that helps, please let me know if you have further questions.