Do you mean you want a platform which is say 4 blocks long to be made up of LEFT-MIDDLE-MIDDLE-RIGHT block? If so you can use a loop from 1 to platform length if/then type statements to determine which kind of block to show based on how long the platform is
loopindex = 1 then create "LEFT" block
loopindex >1 and < platform length then create "MIDDLE" block
loopindex = platform length then create "RIGHT" block
Or did I misunderstand the question again?