It's a question I've seen a couple places. You can move any block anywhere on the chain and it will automatically shuffle things around. SO, to insert a new block, just go to an empty block and create your new block. Then hit ACTION button and it will "lift" the new block. Now move it up the chain with the joystick to wherever you want it and just drop it in. Everything shuffles to make room for it. Press the joystick knob to drop it into place.
We're accustomed to making space first then creating; Just create the block anywhere there's room and move it to where you want.