You could try moving each piece left by 100*sin(self.angle) pixels or something. You'll probably want to tweak 100 till it looks right.
Here's the general idea below. If there are still gaps increase 100 to something bigger.
global number prevAngle=0
global number prevX=0
global number prevY=240
global number turn=0
start of layout
repeat 10 times
set turn to random(-10,10)
create tiledbg at (tiledbg.x, tiledbg.y)
tiledbg: set angle to prevAngle+turn
tiledbg: move tiledbg.width-100*sin(turn) pixels at prevAngle degrees
set prevAngle to tiledbg.angle
set prevX to tiledbg.x
set prevY to tiledbg.y