At first, I bough extra compartment inserts. But realized shortly after getting my first 3D printer, that designing and printing my own was going to be cheaper and quicker. 

The dimensions of the smallest box are specified as 39mm wide x 55mm deep x 47mm height; for 3D printing, the better dimensions seemed to be 38mm x 53mm x 46mm. The feet were inset from the outer edge so that they nestled inside the raised notches on the bottom of the box. First design was to avoid printing the overhang with support so the box and foot were separate (far-left and second from left) and use CA glue to bond them together (middle). 

This worked out but ended up being inaccurate and a bit missy so the subsequent designs were one piece. Solid bottom ended up being equally as good as printing just the four feet as the print required support material underneath anyways.

Like to 3D print? Check out Thingiverse or OnShape.

Reference: Raaco's A9-1 which you can buy from element14 and others.