This is my first time uploading anything on printables, if I messed something up, please bring it to my attention and I'll try my best to fix it. 

I was getting kind of tired of having to line up the riser every time I moved my laptop, so I whipped something up real quickly in cad in order to deal with it. I made it fully parametric so you can change the distance between the risers to fit your laptop. The spacer fits in the little nook made by the middle cut-out, it's not the most secure, but it stays in place. Below is a description of what the different parameters change:

Slot_Tolerance: Self-explanatory, it's multiplied by two in the sketch. (if you input 0.2, the actual slot width will be 20.4 in order to have 0.2 mm on both sides)

Spacer_Distance: The main thing you'll want to change, changes the distance between the inside edges of the risers. (if you have 0.2 mm tolerance and 100 mm as spacer distance, the actual full length of the spacer will be 140.8 mm (100+(2*(20+(0.2*2))))

Slot_Length: How long the slot is, bigger is more surface area in contact with the riser.

Height: Changes how much the slots grip the risers. (max of 6mm I think)

Slot_Thickness: If your slot keeps snapping, this can make the slots thiccer.

Chamfer: I included this so that if you want to make the chamfers smaller you can.

I printed my spacer on the long edge so that the slot wouldn't snap, if you're having troubles with bed adhesion consider printing it flat side down.