I'm new to Construct, but it seems to me that collision on Sprite objects can be turned off or on.
It would be most appropriate to treat each column as a static pile (i.e. no movement) - then only the top of the static pile would need collision enabled.
Items that fall in from the top would have collision enabled by default.
When a block lands, you'd turn off collision on the box it landed on, and disable movement on both.
This idea could be extended such that when the full grid falls in (if that's how your level starts), only the first falling object would have collision enabled. As the box lands, simply enable collision on the next up the falling chain.
Where blocks are removed from the middle, you'd have to treat the bottom bit as a static pile, and the top as a falling pile - indeed if blocks are removed such that two holes are made in one column, you'd still only have to treat all of the falling items as one stack, not several.
Hope this makes sense.