In Construct 1 the platform behavior had an action that allowed you to select any solids that you wanted to ignore collisions with, but this feature is not in Construct 2 at the moment.
It would be great to have a "ignore collision with selected solid" feature in construct 2 that would work with all behaviors, but until then these are the workarounds you can use to achieve that same effect.
1. Use Paco's Extended Platform behavior
2. Use the default Physics behavior to create your own movement, then use the "Enable/disable collisions" action to choose which solids to ignore.
3. Make your own movement using R0J0hound's Chipmunk Physics behavior, then use the collision filtering feature to ignore selected solids.
4. Make your own movement using the custom movement behavior or without using behaviors at all.
5. Make your own "stop movement" or "push out" system that could push the objects out of selected solids when overlapping them.
6. Use R0J0hound's collision filtering example that was made using events.
Link: https://www.dropbox.com/s/i1vr8srq201gw ... .capx?dl=1
7. Use ruskul's modified platform behavior.
Link to thread: ignoring-specific-solids-using-the-platform-behavior_t167299
Link to behavior: http://www.mediafire.com/download/q5y7l ... dified.zip
Link to example cap: http://www.mediafire.com/download/r9c2l ... tform.capx
If you know any other workarounds, please tell me so I can add them to this list.