BTW: Are there plans to have C2 to diferentiate between different layers of physic? So that one could build "crossovers" and "underground" paths? like Bridges and tunnels?
You can already do this using variables.
WARNING, pseudo code incoming:
-Ball is on the "lower level" -> set variable "ball-level" to 0
-If variable "ball-level" is 0 and ball collides with "upper level" -> Do not collide with "upper level"
-Ball touches "start of ramp" -> set variable "ball-level" to 1
-If variable "ball-level" is 1 and ball collides with "upper level" -> collide with "upper level"
More-or-less you would use something along those lines so that the ball will only interact with objects it's supposed to at the time. You would need to plan out your table nicely and figure out where and how you would set the variables for the ball, including if it rolls backwards (because it didn't have enough velocity). IT could take some tweaking to get it right but that would easily work.