It should be relatively easy..
From the top of my head it should be something like this:
you'd want to create two platforms on the same y..
Set the first to a random x-coordinate and the second to the x coordinate of the first + the amount it has to be moved to create the wanted gap.
if you want to create new platforms at say 200px distance you could make an event that says something like:
if platform.y > viewporttop(0)+150 - create new platform at platform.y-200
this event should be triggered once offcourse..