I made some modifications to the models for the back. I scaled them by two in the z direction (out from the back, not true Z-axis for some of the models), and then lopped off about 2 1/2 cm. I did that so that the holder for the tablet was stretched enough to hold the laptop. I also cut a sizeable chunk out of the center of the back to make room for the laptop, and added braces for structural stability.

Next step is to design covers for the sides, with holes for fans. Don't worry, the sudden change in thickness from the back to the hips will be fixed (I've got lots more stuff to cram in there, but I'll make it slope back to where it should be, that'll give him a backpack-type look I think).