I've tried to do the same - I would also really like an option in the properties to make the platform object only interact with objects on its layer.
The only workarounds I've found or thought of are to either:
1: use custom movement instead, requires a lot of events
2: (haven't tried this, might not work) do something wacky using a combination of platform without solids and use custom movement for the collisions and events for the jumping (this will muck around with the 'is jumping' and such, though and probably is complex enough that you might as well use the custom movement entirely)
3: actually have all the different layers displaced so none overlap, then have 'fakes' projected at the proper location.
This is a feature I've wanted since the early days of CC. Ashley, any chance this could be put on that huge todo list of yours? ^^